diff --git a/include/itertools.hpp b/include/itertools.hpp
index f7d2b430..b1d0d32a 100644
--- a/include/itertools.hpp
+++ b/include/itertools.hpp
@@ -8,6 +8,7 @@
 #include <stddef.h>
 #include <string>
 #include <tuple>
+#include <type_traits>
 #include <unordered_map>
 #include <utility>
 
diff --git a/include/util.hpp b/include/util.hpp
index f87cb343..07c6ddc2 100644
--- a/include/util.hpp
+++ b/include/util.hpp
@@ -4,8 +4,9 @@
 #define RGBDS_UTIL_HPP
 
 #include <algorithm>
-#include <ctype.h>
+#include <ctype.h> // toupper
 #include <numeric>
+#include <optional>
 #include <stddef.h>
 #include <stdint.h>
 #include <string>
@@ -13,12 +14,21 @@
 
 #include "helpers.hpp"
 
+enum NumberBase {
+	BASE_AUTO = 0,
+	BASE_2 = 2,
+	BASE_8 = 8,
+	BASE_10 = 10,
+	BASE_16 = 16,
+};
+
 bool isNewline(int c);
 bool isBlankSpace(int c);
 bool isWhitespace(int c);
 bool isPrintable(int c);
 bool isLetter(int c);
 bool isDigit(int c);
+bool isBinDigit(int c);
 bool isOctDigit(int c);
 bool isHexDigit(int c);
 bool isAlphanumeric(int c);
@@ -27,6 +37,8 @@ bool startsIdentifier(int c);
 bool continuesIdentifier(int c);
 
 uint8_t parseHexDigit(int c);
+std::optional<uint64_t> parseNumber(char const *&str, NumberBase base = BASE_AUTO);
+std::optional<uint64_t> parseWholeNumber(char const *str, NumberBase base = BASE_AUTO);
 
 char const *printChar(int c);
 
diff --git a/include/verbosity.hpp b/include/verbosity.hpp
index 45e0fd33..f7658880 100644
--- a/include/verbosity.hpp
+++ b/include/verbosity.hpp
@@ -3,6 +3,8 @@
 #ifndef RGBDS_VERBOSITY_HPP
 #define RGBDS_VERBOSITY_HPP
 
+#include <stdio.h>
+
 #include "style.hpp"
 
 // This macro does not evaluate its arguments unless the condition is true.
diff --git a/src/asm/format.cpp b/src/asm/format.cpp
index a1b3ec5d..cc9cb541 100644
--- a/src/asm/format.cpp
+++ b/src/asm/format.cpp
@@ -11,24 +11,21 @@
 #include <string.h>
 #include <string>
 
-#include "util.hpp" // isDigit
+#include "util.hpp" // parseNumber
 
 #include "asm/main.hpp" // options
 #include "asm/warning.hpp"
 
-static size_t parseNumber(char const *spec, size_t &value) {
-	size_t i = 0;
-
-	value = 0;
-	for (; isDigit(spec[i]); ++i) {
-		value = value * 10 + (spec[i] - '0');
-	}
-
-	return i;
-}
-
 size_t FormatSpec::parseSpec(char const *spec) {
 	size_t i = 0;
+
+	auto parseSpecNumber = [&spec, &i]() {
+		char const *end = &spec[i];
+		size_t number = parseNumber(end, BASE_10).value_or(0);
+		i += end - &spec[i];
+		return number;
+	};
+
 	// <sign>
 	if (char c = spec[i]; c == ' ' || c == '+') {
 		++i;
@@ -51,19 +48,19 @@ size_t FormatSpec::parseSpec(char const *spec) {
 	}
 	// <width>
 	if (isDigit(spec[i])) {
-		i += parseNumber(&spec[i], width);
+		width = parseSpecNumber();
 	}
 	// <frac>
 	if (spec[i] == '.') {
 		++i;
 		hasFrac = true;
-		i += parseNumber(&spec[i], fracWidth);
+		fracWidth = parseSpecNumber();
 	}
 	// <prec>
 	if (spec[i] == 'q') {
 		++i;
 		hasPrec = true;
-		i += parseNumber(&spec[i], precision);
+		precision = parseSpecNumber();
 	}
 	// <type>
 	switch (char c = spec[i]; c) {
diff --git a/src/asm/lexer.cpp b/src/asm/lexer.cpp
index a4dff1de..583a21fa 100644
--- a/src/asm/lexer.cpp
+++ b/src/asm/lexer.cpp
@@ -1009,8 +1009,8 @@ static bool isValidDigit(char c) {
 	return isAlphanumeric(c) || c == '.' || c == '#' || c == '@';
 }
 
-static bool isBinDigit(int c) {
-	return c == '0' || c == '1' || c == options.binDigits[0] || c == options.binDigits[1];
+static bool isCustomBinDigit(int c) {
+	return isBinDigit(c) || c == options.binDigits[0] || c == options.binDigits[1];
 }
 
 static bool checkDigitErrors(char const *digits, size_t n, char const *type) {
@@ -1078,7 +1078,7 @@ static uint32_t readBinaryNumber(char const *prefix) {
 		if (value > (UINT32_MAX - bit) / 2) {
 			warning(WARNING_LARGE_CONSTANT, "Integer constant is too large");
 			// Discard any additional digits
-			skipChars([](int d) { return isBinDigit(d) || d == '_'; });
+			skipChars([](int d) { return isCustomBinDigit(d) || d == '_'; });
 			return 0;
 		}
 		value = value * 2 + bit;
@@ -1836,7 +1836,7 @@ static Token yylex_NORMAL() {
 
 		case '%': // Either %=, MOD, or a binary constant
 			c = peek();
-			if (isBinDigit(c) || c == '_') {
+			if (isCustomBinDigit(c) || c == '_') {
 				return Token(T_(NUMBER), readBinaryNumber("'%'"));
 			}
 			return oneOrTwo('=', T_(POP_MODEQ), T_(OP_MOD));
diff --git a/src/asm/main.cpp b/src/asm/main.cpp
index b477309c..303e8386 100644
--- a/src/asm/main.cpp
+++ b/src/asm/main.cpp
@@ -6,6 +6,7 @@
 #include <errno.h>
 #include <inttypes.h>
 #include <memory>
+#include <optional>
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -299,6 +300,8 @@ int main(int argc, char *argv[]) {
 	// https://reproducible-builds.org/docs/source-date-epoch/
 	time_t now = time(nullptr);
 	if (char const *sourceDateEpoch = getenv("SOURCE_DATE_EPOCH"); sourceDateEpoch) {
+		// Use `strtoul`, not `parseWholeNumber`, because SOURCE_DATE_EPOCH does
+		// not conventionally support our custom base prefixes
 		now = static_cast<time_t>(strtoul(sourceDateEpoch, nullptr, 0));
 	}
 	sym_Init(now);
@@ -378,51 +381,41 @@ int main(int argc, char *argv[]) {
 			fstk_AddPreIncludeFile(musl_optarg);
 			break;
 
-		case 'p': {
-			char *endptr;
-			unsigned long padByte = strtoul(musl_optarg, &endptr, 0);
-
-			if (musl_optarg[0] == '\0' || *endptr != '\0') {
+		case 'p':
+			if (std::optional<uint64_t> padByte = parseWholeNumber(musl_optarg); !padByte) {
 				fatal("Invalid argument for option '-p'");
-			}
-
-			if (padByte > 0xFF) {
+			} else if (*padByte > 0xFF) {
 				fatal("Argument for option '-p' must be between 0 and 0xFF");
+			} else {
+				opt_P(*padByte);
 			}
-
-			opt_P(padByte);
 			break;
-		}
 
 		case 'Q': {
 			char const *precisionArg = musl_optarg;
 			if (precisionArg[0] == '.') {
 				++precisionArg;
 			}
-			char *endptr;
-			unsigned long precision = strtoul(precisionArg, &endptr, 0);
 
-			if (precisionArg[0] == '\0' || *endptr != '\0') {
+			if (std::optional<uint64_t> precision = parseWholeNumber(precisionArg); !precision) {
 				fatal("Invalid argument for option '-Q'");
-			}
-
-			if (precision < 1 || precision > 31) {
+			} else if (*precision < 1 || *precision > 31) {
 				fatal("Argument for option '-Q' must be between 1 and 31");
+			} else {
+				opt_Q(*precision);
 			}
-
-			opt_Q(precision);
 			break;
 		}
 
-		case 'r': {
-			char *endptr;
-			options.maxRecursionDepth = strtoul(musl_optarg, &endptr, 0);
-
-			if (musl_optarg[0] == '\0' || *endptr != '\0') {
+		case 'r':
+			if (std::optional<uint64_t> maxDepth = parseWholeNumber(musl_optarg); !maxDepth) {
 				fatal("Invalid argument for option '-r'");
+			} else if (errno == ERANGE) {
+				fatal("Argument for option '-r' is out of range");
+			} else {
+				options.maxRecursionDepth = *maxDepth;
 			}
 			break;
-		}
 
 		case 's': {
 			// Split "<features>:<name>" so `musl_optarg` is "<features>" and `name` is "<name>"
@@ -459,21 +452,15 @@ int main(int argc, char *argv[]) {
 			warnings.state.warningsEnabled = false;
 			break;
 
-		case 'X': {
-			char *endptr;
-			uint64_t maxErrors = strtoul(musl_optarg, &endptr, 0);
-
-			if (musl_optarg[0] == '\0' || *endptr != '\0') {
+		case 'X':
+			if (std::optional<uint64_t> maxErrors = parseWholeNumber(musl_optarg); !maxErrors) {
 				fatal("Invalid argument for option '-X'");
-			}
-
-			if (maxErrors > UINT64_MAX) {
+			} else if (*maxErrors > UINT64_MAX) {
 				fatal("Argument for option '-X' must be between 0 and %" PRIu64, UINT64_MAX);
+			} else {
+				options.maxErrors = *maxErrors;
 			}
-
-			options.maxErrors = maxErrors;
 			break;
-		}
 
 		case 0: // Long-only options
 			switch (longOpt) {
diff --git a/src/asm/opt.cpp b/src/asm/opt.cpp
index e4249581..08978d41 100644
--- a/src/asm/opt.cpp
+++ b/src/asm/opt.cpp
@@ -2,6 +2,7 @@
 
 #include <errno.h>
 #include <iterator> // std::size
+#include <optional>
 #include <stack>
 #include <stdint.h>
 #include <stdio.h>
@@ -9,8 +10,7 @@
 #include <string.h>
 
 #include "diagnostics.hpp"
-#include "helpers.hpp" // assume
-#include "util.hpp"    // isBlankSpace
+#include "util.hpp"
 
 #include "asm/fstack.hpp"
 #include "asm/lexer.hpp"
@@ -81,50 +81,38 @@ void opt_Parse(char const *s) {
 		}
 		break;
 
-	case 'p': {
-		char *endptr;
-		unsigned long padByte = strtoul(s, &endptr, 0);
-
-		if (s[0] == '\0' || *endptr != '\0') {
+	case 'p':
+		if (std::optional<uint64_t> padByte = parseWholeNumber(s); !padByte) {
 			error("Invalid argument for option 'p'");
-		} else if (padByte > 0xFF) {
+		} else if (*padByte > 0xFF) {
 			error("Argument for option 'p' must be between 0 and 0xFF");
 		} else {
-			opt_P(padByte);
+			opt_P(*padByte);
 		}
 		break;
-	}
 
-	case 'Q': {
+	case 'Q':
 		if (s[0] == '.') {
 			++s; // Skip leading '.'
 		}
-		char *endptr;
-		unsigned long precision = strtoul(s, &endptr, 0);
-
-		if (s[0] == '\0' || *endptr != '\0') {
+		if (std::optional<uint64_t> precision = parseWholeNumber(s); !precision) {
 			error("Invalid argument for option 'Q'");
-		} else if (precision < 1 || precision > 31) {
+		} else if (*precision < 1 || *precision > 31) {
 			error("Argument for option 'Q' must be between 1 and 31");
 		} else {
-			opt_Q(precision);
+			opt_Q(*precision);
 		}
 		break;
-	}
 
-	case 'r': {
-		char *endptr;
-		unsigned long maxRecursionDepth = strtoul(s, &endptr, 0);
-
-		if (s[0] == '\0' || *endptr != '\0') {
+	case 'r':
+		if (std::optional<uint64_t> maxRecursionDepth = parseWholeNumber(s); !maxRecursionDepth) {
 			error("Invalid argument for option 'r'");
 		} else if (errno == ERANGE) {
 			error("Argument for option 'r' is out of range");
 		} else {
-			opt_R(maxRecursionDepth);
+			opt_R(*maxRecursionDepth);
 		}
 		break;
-	}
 
 	case 'W':
 		if (strlen(s) > 0) {
diff --git a/src/backtrace.cpp b/src/backtrace.cpp
index a6061fe8..c113ca7c 100644
--- a/src/backtrace.cpp
+++ b/src/backtrace.cpp
@@ -2,9 +2,11 @@
 
 #include "backtrace.hpp"
 
-#include <stdlib.h> // strtoul
+#include <optional>
+#include <stdint.h>
 
 #include "platform.hpp" // strcasecmp
+#include "util.hpp"     // parseWholeNumber
 
 Tracing tracing;
 
@@ -22,8 +24,10 @@ bool trace_ParseTraceDepth(char const *arg) {
 		tracing.loud = false;
 		return true;
 	} else {
-		char *endptr;
-		tracing.depth = strtoul(arg, &endptr, 0);
-		return arg[0] != '\0' && *endptr == '\0';
+		std::optional<uint64_t> depth = parseWholeNumber(arg);
+		if (depth) {
+			tracing.depth = *depth;
+		}
+		return depth.has_value();
 	}
 }
diff --git a/src/diagnostics.cpp b/src/diagnostics.cpp
index d60a86a6..af3c81dd 100644
--- a/src/diagnostics.cpp
+++ b/src/diagnostics.cpp
@@ -63,25 +63,9 @@ std::pair<WarningState, std::optional<uint32_t>> getInitialWarningState(std::str
 		return {state, std::nullopt};
 	}
 
-	// Is the rest of the string a decimal number?
-	// We want to avoid `strtoul`'s whitespace and sign handling, so we parse manually
+	// If the rest of the string is a decimal number, it's the parameter value
 	char const *ptr = flag.c_str() + equals + 1;
-	uint32_t param = 0;
-	bool overflowed = false;
-
-	for (; isDigit(*ptr); ++ptr) {
-		if (overflowed) {
-			continue;
-		}
-
-		uint32_t c = *ptr - '0';
-		if (param > (UINT32_MAX - c) / 10) {
-			overflowed = true;
-			param = UINT32_MAX;
-			continue;
-		}
-		param = param * 10 + c;
-	}
+	uint64_t param = parseNumber(ptr, BASE_10).value_or(0);
 
 	// If we reached the end of the string, truncate it at the '='
 	if (*ptr == '\0') {
@@ -92,5 +76,5 @@ std::pair<WarningState, std::optional<uint32_t>> getInitialWarningState(std::str
 		}
 	}
 
-	return {state, param};
+	return {state, param > UINT32_MAX ? UINT32_MAX : param};
 }
diff --git a/src/fix/main.cpp b/src/fix/main.cpp
index 526cf59a..c8e74899 100644
--- a/src/fix/main.cpp
+++ b/src/fix/main.cpp
@@ -3,7 +3,9 @@
 #include "fix/main.hpp"
 
 #include <errno.h>
+#include <inttypes.h>
 #include <limits.h>
+#include <optional>
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -16,6 +18,7 @@
 #include "platform.hpp"
 #include "style.hpp"
 #include "usage.hpp"
+#include "util.hpp"
 #include "version.hpp"
 
 #include "fix/fix.hpp"
@@ -89,25 +92,17 @@ static Usage usage = {
 // clang-format on
 
 static void parseByte(uint16_t &output, char name) {
-	if (musl_optarg[0] == 0) {
+	if (musl_optarg[0] == '\0') {
 		fatal("Argument to option '-%c' may not be empty", name);
 	}
 
-	char *endptr;
-	unsigned long value;
-	if (musl_optarg[0] == '$') {
-		value = strtoul(&musl_optarg[1], &endptr, 16);
-	} else {
-		value = strtoul(musl_optarg, &endptr, 0);
-	}
-
-	if (*endptr) {
+	if (std::optional<uint64_t> value = parseWholeNumber(musl_optarg); !value) {
 		fatal("Expected number as argument to option '-%c', got \"%s\"", name, musl_optarg);
 	} else if (value > 0xFF) {
-		fatal("Argument to option '-%c' is larger than 255: %lu", name, value);
+		fatal("Argument to option '-%c' is larger than 255: %" PRIu64, name, *value);
+	} else {
+		output = *value;
 	}
-
-	output = value;
 }
 
 static uint8_t const nintendoLogo[] = {
diff --git a/src/fix/mbc.cpp b/src/fix/mbc.cpp
index 3a211d6c..bf3bbeac 100644
--- a/src/fix/mbc.cpp
+++ b/src/fix/mbc.cpp
@@ -2,9 +2,11 @@
 
 #include "fix/mbc.hpp"
 
+#include <optional>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unordered_map>
 #include <utility>
 
@@ -97,15 +99,11 @@ bool mbc_HasRAM(MbcType type) {
 }
 
 static void skipBlankSpace(char const *&ptr) {
-	while (isBlankSpace(*ptr)) {
-		++ptr;
-	}
+	ptr += strspn(ptr, " \t");
 }
 
 static void skipMBCSpace(char const *&ptr) {
-	while (isBlankSpace(*ptr) || *ptr == '_') {
-		++ptr;
-	}
+	ptr += strspn(ptr, " \t_");
 }
 
 static char normalizeMBCChar(char c) {
@@ -128,53 +126,42 @@ static bool readMBCSlice(char const *&name, char const *expected) {
 }
 
 [[noreturn]]
-static void fatalUnknownMBC(char const *fullName) {
-	fatal("Unknown MBC \"%s\"\n%s", fullName, acceptedMBCNames);
+static void fatalUnknownMBC(char const *name) {
+	fatal("Unknown MBC \"%s\"\n%s", name, acceptedMBCNames);
 }
 
 [[noreturn]]
-static void fatalWrongMBCFeatures(char const *fullName) {
-	fatal("Features incompatible with MBC (\"%s\")\n%s", fullName, acceptedMBCNames);
+static void fatalWrongMBCFeatures(char const *name) {
+	fatal("Features incompatible with MBC (\"%s\")\n%s", name, acceptedMBCNames);
 }
 
 MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor) {
-	char const *fullName = name;
+	char const *ptr = name;
+	skipBlankSpace(ptr); // Trim off leading blank space
 
-	if (!strcasecmp(name, "help") || !strcasecmp(name, "list")) {
+	if (!strcasecmp(ptr, "help") || !strcasecmp(ptr, "list")) {
 		puts(acceptedMBCNames); // Outputs to stdout and appends a newline
 		exit(0);
 	}
 
-	if (isDigit(name[0]) || name[0] == '$') {
-		int base = 0;
-
-		if (name[0] == '$') {
-			++name;
-			base = 16;
+	// Parse numeric MBC and return it as-is (unless it's too large)
+	if (char c = *ptr; isDigit(c) || c == '$' || c == '&' || c == '%') {
+		if (std::optional<uint64_t> mbc = parseWholeNumber(ptr); !mbc) {
+			fatalUnknownMBC(name);
+		} else if (*mbc > 0xFF) {
+			fatal("Specified MBC ID out of range 0-255: \"%s\"", name);
+		} else {
+			return static_cast<MbcType>(*mbc);
 		}
-		// Parse number, and return it as-is (unless it's too large)
-		char *endptr;
-		unsigned long mbc = strtoul(name, &endptr, base);
-
-		if (*endptr) {
-			fatalUnknownMBC(fullName);
-		}
-		if (mbc > 0xFF) {
-			fatal("Specified MBC ID out of range 0-255: \"%s\"", fullName);
-		}
-		return static_cast<MbcType>(mbc);
 	}
 
 	// Begin by reading the MBC type:
 	uint16_t mbc;
-	char const *ptr = name;
-
-	skipBlankSpace(ptr); // Trim off leading blank space
 
 #define tryReadSlice(expected) \
 	do { \
 		if (!readMBCSlice(ptr, expected)) { \
-			fatalUnknownMBC(fullName); \
+			fatalUnknownMBC(name); \
 		} \
 	} while (0)
 
@@ -201,7 +188,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 			case 'c':
 				break;
 			default:
-				fatalUnknownMBC(fullName);
+				fatalUnknownMBC(name);
 			}
 			switch (*ptr++) {
 			case '1':
@@ -223,7 +210,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 				mbc = MBC7_SENSOR_RUMBLE_RAM_BATTERY;
 				break;
 			default:
-				fatalUnknownMBC(fullName);
+				fatalUnknownMBC(name);
 			}
 			break;
 		case 'M':
@@ -232,7 +219,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 			mbc = MMM01;
 			break;
 		default:
-			fatalUnknownMBC(fullName);
+			fatalUnknownMBC(name);
 		}
 		break;
 
@@ -260,33 +247,27 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 			// Parse version
 			skipMBCSpace(ptr);
 			// Major
-			char *endptr;
-			unsigned long val = strtoul(ptr, &endptr, 10);
-
-			if (endptr == ptr) {
+			if (std::optional<uint64_t> major = parseNumber(ptr, BASE_10); !major) {
 				fatal("Failed to parse TPP1 major revision number");
-			}
-			ptr = endptr;
-			if (val != 1) {
+			} else if (*major != 1) {
 				fatal("RGBFIX only supports TPP1 version 1.0");
+			} else {
+				tpp1Major = *major;
 			}
-			tpp1Major = val;
 			tryReadSlice(".");
 			// Minor
-			val = strtoul(ptr, &endptr, 10);
-			if (endptr == ptr) {
+			if (std::optional<uint64_t> minor = parseNumber(ptr, BASE_10); !minor) {
 				fatal("Failed to parse TPP1 minor revision number");
-			}
-			ptr = endptr;
-			if (val > 0xFF) {
+			} else if (*minor > 0xFF) {
 				fatal("TPP1 minor revision number must be 8-bit");
+			} else {
+				tpp1Minor = *minor;
 			}
-			tpp1Minor = val;
 			mbc = TPP1;
 			break;
 		}
 		default:
-			fatalUnknownMBC(fullName);
+			fatalUnknownMBC(name);
 		}
 		break;
 
@@ -301,12 +282,12 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 			mbc = HUC3;
 			break;
 		default:
-			fatalUnknownMBC(fullName);
+			fatalUnknownMBC(name);
 		}
 		break;
 
 	default:
-		fatalUnknownMBC(fullName);
+		fatalUnknownMBC(name);
 	}
 
 	// Read "additional features"
@@ -330,7 +311,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 		// We expect a '+' at this point
 		skipMBCSpace(ptr);
 		if (*ptr++ != '+') {
-			fatalUnknownMBC(fullName);
+			fatalUnknownMBC(name);
 		}
 		skipMBCSpace(ptr);
 
@@ -361,7 +342,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 				features |= RAM;
 				break;
 			default:
-				fatalUnknownMBC(fullName);
+				fatalUnknownMBC(name);
 			}
 			break;
 
@@ -378,7 +359,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 			break;
 
 		default:
-			fatalUnknownMBC(fullName);
+			fatalUnknownMBC(name);
 		}
 	}
 #undef tryReadSlice
@@ -402,7 +383,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 		} else if (features == (RAM | BATTERY)) {
 			mbc += 2;
 		} else if (features) {
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		break;
 
@@ -410,7 +391,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 		if (features == BATTERY) {
 			mbc = MBC2_BATTERY;
 		} else if (features) {
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		break;
 
@@ -434,7 +415,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 		} else if (features == (RAM | BATTERY)) {
 			mbc += 2;
 		} else if (features) {
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		break;
 
@@ -452,7 +433,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 		} else if (features == (RAM | BATTERY)) {
 			mbc += 2;
 		} else if (features) {
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		break;
 
@@ -462,19 +443,19 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 	case HUC3:
 		// No extra features accepted
 		if (features) {
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		break;
 
 	case MBC7_SENSOR_RUMBLE_RAM_BATTERY:
 		if (features != (SENSOR | RUMBLE | RAM | BATTERY)) {
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		break;
 
 	case HUC1_RAM_BATTERY:
 		if (features != (RAM | BATTERY)) { // HuC1 expects RAM+BATTERY
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		break;
 
@@ -495,7 +476,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 			mbc |= 0x01;
 		}
 		if (features & SENSOR) {
-			fatalWrongMBCFeatures(fullName);
+			fatalWrongMBCFeatures(name);
 		}
 		// Multiple rumble speeds imply rumble
 		if (mbc & 0x01) {
@@ -508,7 +489,7 @@ MbcType mbc_ParseName(char const *name, uint8_t &tpp1Major, uint8_t &tpp1Minor)
 
 	// If there is still something left, error out
 	if (*ptr) {
-		fatalUnknownMBC(fullName);
+		fatalUnknownMBC(name);
 	}
 
 	return static_cast<MbcType>(mbc);
diff --git a/src/gfx/main.cpp b/src/gfx/main.cpp
index 201e4c47..69c736bc 100644
--- a/src/gfx/main.cpp
+++ b/src/gfx/main.cpp
@@ -3,10 +3,10 @@
 #include "gfx/main.hpp"
 
 #include <algorithm>
-#include <ctype.h>
 #include <errno.h>
 #include <inttypes.h>
 #include <ios>
+#include <optional>
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -122,76 +122,19 @@ static Usage usage = {
 
 // Parses a number at the beginning of a string, moving the pointer to skip the parsed characters.
 // Returns the provided errVal on error.
-static uint16_t parseNumber(char *&string, char const *errPrefix, uint16_t errVal = UINT16_MAX) {
-	uint8_t base = 10;
-	if (*string == '\0') {
+static uint16_t readNumber(char const *&str, char const *errPrefix, uint16_t errVal = UINT16_MAX) {
+	if (std::optional<uint64_t> number = parseNumber(str); !number) {
 		error("%s: expected number, but found nothing", errPrefix);
 		return errVal;
-	} else if (*string == '$') {
-		base = 16;
-		++string;
-	} else if (*string == '%') {
-		base = 2;
-		++string;
-	} else if (*string == '0' && string[1] != '\0') {
-		// Check if we have a "0x" or "0b" here
-		if (string[1] == 'x' || string[1] == 'X') {
-			base = 16;
-			string += 2;
-		} else if (string[1] == 'b' || string[1] == 'B') {
-			base = 2;
-			string += 2;
-		}
-	}
-
-	// Turns a digit into its numeric value in the current base, if it has one.
-	// Maximum is inclusive. The string_view is modified to "consume" all digits.
-	// Returns 255 on parse failure (including wrong char for base), in which case
-	// the string_view may be pointing on garbage.
-	auto charIndex = [&base](unsigned char c) -> uint8_t {
-		unsigned char index = c - '0'; // Use wrapping semantics
-		if (base == 2 && index >= 2) {
-			return 255;
-		} else if (index < 10) {
-			return index;
-		} else if (base != 16) {
-			return 255; // Letters are only valid in hex
-		}
-		index = tolower(c) - 'a'; // OK because we pass an `unsigned char`
-		if (index < 6) {
-			return index + 10;
-		}
-		return 255;
-	};
-
-	if (charIndex(*string) == 255) {
-		error(
-		    "%s: expected digit%s, but found nothing", errPrefix, base != 10 ? " after base" : ""
-		);
+	} else if (*number > UINT16_MAX) {
+		error("%s: the number is too large!", errPrefix);
 		return errVal;
+	} else {
+		return *number;
 	}
-	uint16_t number = 0;
-	do {
-		// Read a character, and check if it's valid in the given base
-		uint8_t index = charIndex(*string);
-		if (index == 255) {
-			break; // Found an invalid character, end
-		}
-		++string;
-
-		number *= base;
-		number += index;
-		// The lax check covers the addition on top of the multiplication
-		if (number >= UINT16_MAX / base) {
-			error("%s: the number is too large!", errPrefix);
-			return errVal;
-		}
-	} while (*string != '\0'); // No more characters?
-
-	return number;
 }
 
-static void skipBlankSpace(char *&arg) {
+static void skipBlankSpace(char const *&arg) {
 	arg += strspn(arg, " \t");
 }
 
@@ -263,7 +206,7 @@ static std::vector<size_t> readAtFile(std::string const &path, std::vector<char>
 // to an "at-file" path if one is encountered.
 static char *parseArgv(int argc, char *argv[]) {
 	for (int ch; (ch = musl_getopt_long_only(argc, argv, optstring, longopts, nullptr)) != -1;) {
-		char *arg = musl_optarg; // Make a copy for scanning
+		char const *arg = musl_optarg; // Make a copy for scanning
 
 		switch (ch) {
 		case 'A':
@@ -283,7 +226,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 'b': {
-			uint16_t number = parseNumber(arg, "Bank 0 base tile ID", 0);
+			uint16_t number = readNumber(arg, "Bank 0 base tile ID", 0);
 			if (number >= 256) {
 				error("Bank 0 base tile ID must be below 256");
 			} else {
@@ -303,7 +246,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			}
 			++arg; // Skip comma
 			skipBlankSpace(arg);
-			number = parseNumber(arg, "Bank 1 base tile ID", 0);
+			number = readNumber(arg, "Bank 1 base tile ID", 0);
 			if (number >= 256) {
 				error("Bank 1 base tile ID must be below 256");
 			} else {
@@ -346,7 +289,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 'd':
-			options.bitDepth = parseNumber(arg, "Bit depth", 2);
+			options.bitDepth = readNumber(arg, "Bit depth", 2);
 			if (*arg != '\0') {
 				error("Bit depth ('-b') argument must be a valid number, not \"%s\"", musl_optarg);
 			} else if (options.bitDepth != 1 && options.bitDepth != 2) {
@@ -368,7 +311,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 'L':
-			options.inputSlice.left = parseNumber(arg, "Input slice left coordinate");
+			options.inputSlice.left = readNumber(arg, "Input slice left coordinate");
 			if (options.inputSlice.left > INT16_MAX) {
 				error("Input slice left coordinate is out of range!");
 				break;
@@ -380,7 +323,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			}
 			++arg;
 			skipBlankSpace(arg);
-			options.inputSlice.top = parseNumber(arg, "Input slice upper coordinate");
+			options.inputSlice.top = readNumber(arg, "Input slice upper coordinate");
 			skipBlankSpace(arg);
 			if (*arg != ':') {
 				error("Missing colon after upper coordinate in \"%s\"", musl_optarg);
@@ -388,7 +331,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			}
 			++arg;
 			skipBlankSpace(arg);
-			options.inputSlice.width = parseNumber(arg, "Input slice width");
+			options.inputSlice.width = readNumber(arg, "Input slice width");
 			skipBlankSpace(arg);
 			if (options.inputSlice.width == 0) {
 				error("Input slice width may not be 0!");
@@ -399,7 +342,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			}
 			++arg;
 			skipBlankSpace(arg);
-			options.inputSlice.height = parseNumber(arg, "Input slice height");
+			options.inputSlice.height = readNumber(arg, "Input slice height");
 			if (options.inputSlice.height == 0) {
 				error("Input slice height may not be 0!");
 			}
@@ -409,7 +352,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 'l': {
-			uint16_t number = parseNumber(arg, "Base palette ID", 0);
+			uint16_t number = readNumber(arg, "Base palette ID", 0);
 			if (*arg != '\0') {
 				error("Base palette ID must be a valid number, not \"%s\"", musl_optarg);
 			} else if (number >= 256) {
@@ -430,7 +373,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 'N':
-			options.maxNbTiles[0] = parseNumber(arg, "Number of tiles in bank 0", 256);
+			options.maxNbTiles[0] = readNumber(arg, "Number of tiles in bank 0", 256);
 			if (options.maxNbTiles[0] > 256) {
 				error("Bank 0 cannot contain more than 256 tiles");
 			}
@@ -448,7 +391,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			}
 			++arg; // Skip comma
 			skipBlankSpace(arg);
-			options.maxNbTiles[1] = parseNumber(arg, "Number of tiles in bank 1", 256);
+			options.maxNbTiles[1] = readNumber(arg, "Number of tiles in bank 1", 256);
 			if (options.maxNbTiles[1] > 256) {
 				error("Bank 1 cannot contain more than 256 tiles");
 			}
@@ -462,7 +405,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 'n': {
-			uint16_t number = parseNumber(arg, "Number of palettes", 256);
+			uint16_t number = readNumber(arg, "Number of palettes", 256);
 			if (*arg != '\0') {
 				error("Number of palettes ('-n') must be a valid number, not \"%s\"", musl_optarg);
 			}
@@ -513,7 +456,7 @@ static char *parseArgv(int argc, char *argv[]) {
 
 		case 'r':
 			localOptions.reverse = true;
-			options.reversedWidth = parseNumber(arg, "Reversed image stride");
+			options.reversedWidth = readNumber(arg, "Reversed image stride");
 			if (*arg != '\0') {
 				error(
 				    "Reversed image stride ('-r') must be a valid number, not \"%s\"", musl_optarg
@@ -522,7 +465,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 's':
-			options.nbColorsPerPal = parseNumber(arg, "Number of colors per palette", 4);
+			options.nbColorsPerPal = readNumber(arg, "Number of colors per palette", 4);
 			if (*arg != '\0') {
 				error("Palette size ('-s') must be a valid number, not \"%s\"", musl_optarg);
 			}
@@ -564,7 +507,7 @@ static char *parseArgv(int argc, char *argv[]) {
 			break;
 
 		case 'x':
-			options.trim = parseNumber(arg, "Number of tiles to trim", 0);
+			options.trim = readNumber(arg, "Number of tiles to trim", 0);
 			if (*arg != '\0') {
 				error("Tile trim ('-x') argument must be a valid number, not \"%s\"", musl_optarg);
 			}
diff --git a/src/gfx/pal_packing.cpp b/src/gfx/pal_packing.cpp
index 0f5dbe74..b9749400 100644
--- a/src/gfx/pal_packing.cpp
+++ b/src/gfx/pal_packing.cpp
@@ -9,6 +9,7 @@
 #include <numeric>
 #include <optional>
 #include <queue>
+#include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <type_traits>
diff --git a/src/link/lexer.cpp b/src/link/lexer.cpp
index 5159ab7e..9f6fcf28 100644
--- a/src/link/lexer.cpp
+++ b/src/link/lexer.cpp
@@ -106,10 +106,6 @@ static yy::parser::symbol_type parseDecNumber(int c) {
 	return yy::parser::make_number(number);
 }
 
-static bool isBinDigit(int c) {
-	return c == '0' || c == '1';
-}
-
 static yy::parser::symbol_type parseBinNumber(char const *prefix) {
 	LexerStackEntry &context = lexerStack.back();
 	int c = context.file.sgetc();
@@ -167,7 +163,7 @@ static yy::parser::symbol_type parseHexNumber(char const *prefix) {
 	return yy::parser::make_number(number);
 }
 
-static yy::parser::symbol_type parseNumber(int c) {
+static yy::parser::symbol_type parseAnyNumber(int c) {
 	LexerStackEntry &context = lexerStack.back();
 	if (c == '0') {
 		switch (context.file.sgetc()) {
@@ -265,7 +261,7 @@ yy::parser::symbol_type yylex() {
 	} else if (c == '&') {
 		return parseOctNumber("'&'");
 	} else if (isDigit(c)) {
-		return parseNumber(c);
+		return parseAnyNumber(c);
 	} else if (isLetter(c)) {
 		std::string keyword = readKeyword(c);
 
diff --git a/src/link/main.cpp b/src/link/main.cpp
index c7cb0b75..a95ec15f 100644
--- a/src/link/main.cpp
+++ b/src/link/main.cpp
@@ -4,6 +4,7 @@
 
 #include <inttypes.h>
 #include <limits.h>
+#include <optional>
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -265,21 +266,18 @@ static void parseScrambleSpec(char *spec) {
 
 		uint16_t limit = search->second.second;
 		if (regionSize) {
-			char *endptr;
-			unsigned long value = strtoul(regionSize, &endptr, 0);
-
-			if (*endptr != '\0') {
+			char const *ptr = regionSize + skipBlankSpace(regionSize);
+			if (std::optional<uint64_t> value = parseWholeNumber(ptr); !value) {
 				fatal("Invalid region size limit \"%s\" for option '-S'", regionSize);
-			}
-			if (value > limit) {
+			} else if (*value > limit) {
 				fatal(
 				    "%s region size for option '-S' must be between 0 and %" PRIu16,
 				    search->first.c_str(),
 				    limit
 				);
+			} else {
+				limit = *value;
 			}
-
-			limit = value;
 		} else if (search->second.first != &options.scrambleWRAMX) {
 			// Only WRAMX limit can be implied, since ROMX and SRAM size may vary.
 			fatal("Missing %s region size limit for option '-S'", search->first.c_str());
@@ -353,21 +351,16 @@ int main(int argc, char *argv[]) {
 			options.outputFileName = musl_optarg;
 			break;
 
-		case 'p': {
-			char *endptr;
-			unsigned long value = strtoul(musl_optarg, &endptr, 0);
-
-			if (musl_optarg[0] == '\0' || *endptr != '\0') {
+		case 'p':
+			if (std::optional<uint64_t> value = parseWholeNumber(musl_optarg); !value) {
 				fatal("Invalid argument for option '-p'");
-			}
-			if (value > 0xFF) {
+			} else if (*value > 0xFF) {
 				fatal("Argument for option '-p' must be between 0 and 0xFF");
+			} else {
+				options.padValue = *value;
+				options.hasPadValue = true;
 			}
-
-			options.padValue = value;
-			options.hasPadValue = true;
 			break;
-		}
 
 		case 'S':
 			parseScrambleSpec(musl_optarg);
diff --git a/src/link/sdas_obj.cpp b/src/link/sdas_obj.cpp
index 8d4ab11d..78e0835c 100644
--- a/src/link/sdas_obj.cpp
+++ b/src/link/sdas_obj.cpp
@@ -2,9 +2,9 @@
 
 #include "link/sdas_obj.hpp"
 
-#include <ctype.h>
 #include <inttypes.h>
 #include <memory>
+#include <optional>
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
@@ -15,18 +15,13 @@
 #include "helpers.hpp" // assume, literal_strlen
 #include "linkdefs.hpp"
 #include "platform.hpp"
+#include "util.hpp" // parseWholeNumber
 
 #include "link/fstack.hpp"
 #include "link/section.hpp"
 #include "link/symbol.hpp"
 #include "link/warning.hpp"
 
-enum NumberType {
-	HEX = 16, // X
-	DEC = 10, // D
-	OCT = 8,  // Q
-};
-
 struct Location {
 	FileStackNode const *src;
 	uint32_t lineNo;
@@ -84,36 +79,26 @@ static int nextLine(std::vector<char> &lineBuf, Location &where, FILE *file) {
 	}
 }
 
-static uint32_t readNumber(char const *str, char const *&endptr, NumberType base) {
-	for (uint32_t res = 0;;) {
-		static char const *digits = "0123456789ABCDEF";
-		char const *ptr = strchr(digits, toupper(*str));
+static uint64_t readNumber(Location const &where, char const *str, NumberBase base) {
+	std::optional<uint64_t> res = parseWholeNumber(str, base);
 
-		if (!ptr || ptr - digits >= base) {
-			endptr = str;
-			return res;
-		}
-		++str;
-		res = res * base + (ptr - digits);
-	}
-}
-
-static uint32_t parseNumber(Location const &where, char const *str, NumberType base) {
-	if (str[0] == '\0') {
-		fatalAt(where, "Expected number, got empty string");
-	}
-
-	char const *endptr;
-	uint32_t res = readNumber(str, endptr, base);
-
-	if (*endptr != '\0') {
+	if (!res) {
 		fatalAt(where, "Expected number, got \"%s\"", str);
 	}
-	return res;
+	return *res;
 }
 
-static uint8_t parseByte(Location const &where, char const *str, NumberType base) {
-	uint32_t num = parseNumber(where, str, base);
+static uint32_t readInt(Location const &where, char const *str, NumberBase base) {
+	uint64_t num = readNumber(where, str, base);
+
+	if (num > UINT32_MAX) {
+		fatalAt(where, "\"%s\" is not an int", str);
+	}
+	return num;
+}
+
+static uint8_t readByte(Location const &where, char const *str, NumberBase base) {
+	uint64_t num = readNumber(where, str, base);
 
 	if (num > UINT8_MAX) {
 		fatalAt(where, "\"%s\" is not a byte", str);
@@ -184,18 +169,18 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 	int lineType = nextLine(line, where, file);
 
 	// The first letter (thus, the line type) identifies the integer type
-	NumberType numberType;
+	NumberBase numberBase;
 	switch (lineType) {
 	case EOF:
 		fatalAt(where, "SDCC object only contains comments and empty lines");
 	case 'X':
-		numberType = HEX;
+		numberBase = BASE_16;
 		break;
 	case 'D':
-		numberType = DEC;
+		numberBase = BASE_10;
 		break;
 	case 'Q':
-		numberType = OCT;
+		numberBase = BASE_8;
 		break;
 	default:
 		fatalAt(
@@ -239,12 +224,12 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 	// Expected format: "A areas S global symbols"
 
 	getToken(line.data(), "Empty 'H' line");
-	uint32_t expectedNbAreas = parseNumber(where, token, numberType);
+	uint32_t expectedNbAreas = readInt(where, token, numberBase);
 
 	expectToken("areas", 'H');
 
 	getToken(nullptr, "'H' line is too short");
-	uint32_t expectedNbSymbols = parseNumber(where, token, numberType);
+	uint32_t expectedNbSymbols = readInt(where, token, numberBase);
 	fileSymbols.reserve(expectedNbSymbols);
 
 	expectToken("global", 'H');
@@ -296,7 +281,7 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 
 			getToken(nullptr, "'A' line is too short");
 
-			uint32_t tmp = parseNumber(where, token, numberType);
+			uint32_t tmp = readInt(where, token, numberBase);
 
 			if (tmp > UINT16_MAX) {
 				fatalAt(
@@ -310,7 +295,7 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 			expectToken("flags", 'A');
 
 			getToken(nullptr, "'A' line is too short");
-			tmp = parseNumber(where, token, numberType);
+			tmp = readInt(where, token, numberBase);
 			if (tmp & (1 << AREA_PAGING)) {
 				fatalAt(where, "Paging is not supported");
 			}
@@ -329,7 +314,7 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 			expectToken("addr", 'A');
 
 			getToken(nullptr, "'A' line is too short");
-			tmp = parseNumber(where, token, numberType);
+			tmp = readInt(where, token, numberBase);
 			curSection->org = tmp; // Truncation keeps the address portion only
 			curSection->bank = tmp >> 16;
 
@@ -386,7 +371,7 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 
 			getToken(nullptr, "'S' line is too short");
 
-			if (int32_t value = parseNumber(where, &token[3], numberType); !fileSections.empty()) {
+			if (int32_t value = readInt(where, &token[3], numberBase); !fileSections.empty()) {
 				// Symbols in sections are labels; their value is an offset
 				Section *section = fileSections.back().section.get();
 				if (section->isAddressFixed) {
@@ -465,7 +450,7 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 
 			data.clear();
 			for (token = strtok(line.data(), delim); token; token = strtok(nullptr, delim)) {
-				data.push_back(parseByte(where, token, numberType));
+				data.push_back(readByte(where, token, numberBase));
 			}
 
 			if (data.size() < addrSize) {
@@ -487,9 +472,9 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 			uint16_t areaIdx;
 
 			getToken(nullptr, "'R' line is too short");
-			areaIdx = parseByte(where, token, numberType);
+			areaIdx = readByte(where, token, numberBase);
 			getToken(nullptr, "'R' line is too short");
-			areaIdx |= static_cast<uint16_t>(parseByte(where, token, numberType)) << 8;
+			areaIdx |= static_cast<uint16_t>(readByte(where, token, numberBase)) << 8;
 			if (areaIdx >= fileSections.size()) {
 				fatalAt(
 				    where,
@@ -549,16 +534,16 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 			// appropriate RPN expression (depending on flags), plus an addition for the
 			// bytes being patched over.
 			while ((token = strtok(nullptr, delim)) != nullptr) {
-				uint16_t flags = parseByte(where, token, numberType);
+				uint16_t flags = readByte(where, token, numberBase);
 
 				if ((flags & 0xF0) == 0xF0) {
 					getToken(nullptr, "Incomplete relocation");
 					flags = (flags & 0x0F)
-					        | static_cast<uint16_t>(parseByte(where, token, numberType)) << 4;
+					        | static_cast<uint16_t>(readByte(where, token, numberBase)) << 4;
 				}
 
 				getToken(nullptr, "Incomplete relocation");
-				uint8_t offset = parseByte(where, token, numberType);
+				uint8_t offset = readByte(where, token, numberBase);
 
 				if (offset < addrSize) {
 					fatalAt(
@@ -578,10 +563,10 @@ void sdobj_ReadFile(FileStackNode const &src, FILE *file, std::vector<Symbol> &f
 				}
 
 				getToken(nullptr, "Incomplete relocation");
-				uint16_t idx = parseByte(where, token, numberType);
+				uint16_t idx = readByte(where, token, numberBase);
 
 				getToken(nullptr, "Incomplete relocation");
-				idx |= static_cast<uint16_t>(parseByte(where, token, numberType));
+				idx |= static_cast<uint16_t>(readByte(where, token, numberBase));
 
 				// Loudly fail on unknown flags
 				if (flags & (1 << RELOC_ZPAGE | 1 << RELOC_NPAGE)) {
diff --git a/src/util.cpp b/src/util.cpp
index c24d3249..a3bac118 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -2,8 +2,11 @@
 
 #include "util.hpp"
 
+#include <errno.h>
+#include <optional>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h> // strspn
 
 #include "helpers.hpp" // assume
 
@@ -31,6 +34,10 @@ bool isDigit(int c) {
 	return c >= '0' && c <= '9';
 }
 
+bool isBinDigit(int c) {
+	return c == '0' || c == '1';
+}
+
 bool isOctDigit(int c) {
 	return c >= '0' && c <= '7';
 }
@@ -64,6 +71,97 @@ uint8_t parseHexDigit(int c) {
 	}
 }
 
+// Parses a number from a string, moving the pointer to skip the parsed characters.
+std::optional<uint64_t> parseNumber(char const *&str, NumberBase base) {
+	// Identify the base if not specified
+	// Does *not* support '+' or '-' sign prefix (unlike `strtoul` and `std::from_chars`)
+	if (base == BASE_AUTO) {
+		// Skips leading blank space (like `strtoul`)
+		str += strspn(str, " \t");
+
+		// Supports traditional ("0b", "0o", "0x") and RGBASM ('%', '&', '$') base prefixes
+		switch (str[0]) {
+		case '%':
+			base = BASE_2;
+			++str;
+			break;
+		case '&':
+			base = BASE_8;
+			++str;
+			break;
+		case '$':
+			base = BASE_16;
+			++str;
+			break;
+		case '0':
+			switch (str[1]) {
+			case 'B':
+			case 'b':
+				base = BASE_2;
+				str += 2;
+				break;
+			case 'O':
+			case 'o':
+				base = BASE_8;
+				str += 2;
+				break;
+			case 'X':
+			case 'x':
+				base = BASE_16;
+				str += 2;
+				break;
+			default:
+				base = BASE_10;
+				break;
+			}
+			break;
+		default:
+			base = BASE_10;
+			break;
+		}
+	}
+	assume(base != BASE_AUTO);
+
+	// Get the digit-condition function corresponding to the base
+	bool (*canParseDigit)(int c) = base == BASE_2    ? isBinDigit
+	                               : base == BASE_8  ? isOctDigit
+	                               : base == BASE_10 ? isDigit
+	                               : base == BASE_16 ? isHexDigit
+	                                                 : nullptr; // LCOV_EXCL_LINE
+	assume(canParseDigit != nullptr);
+
+	char const * const startDigits = str;
+
+	// Parse the number one digit at a time
+	// Does *not* support '_' digit separators
+	uint64_t result = 0;
+	for (; canParseDigit(str[0]); ++str) {
+		uint8_t digit = parseHexDigit(str[0]);
+		if (result > (UINT64_MAX - digit) / base) {
+			// Skip remaining digits and set errno = ERANGE on overflow
+			while (canParseDigit(str[0])) {
+				++str;
+			}
+			result = UINT64_MAX;
+			errno = ERANGE;
+			break;
+		}
+		result = result * base + digit;
+	}
+
+	// Return the parsed number if there were any digit characters
+	if (str - startDigits == 0) {
+		return std::nullopt;
+	}
+	return result;
+}
+
+// Parses a number from an entire string, returning nothing if there are more unparsed characters.
+std::optional<uint64_t> parseWholeNumber(char const *str, NumberBase base) {
+	std::optional<uint64_t> result = parseNumber(str, base);
+	return str[0] == '\0' ? result : std::nullopt;
+}
+
 char const *printChar(int c) {
 	// "'A'" + '\0': 4 bytes
 	// "'\\n'" + '\0': 5 bytes
diff --git a/test/gfx/warn_group_output.png b/test/gfx/warn_group_output.png
new file mode 100644
index 00000000..3233c135
Binary files /dev/null and b/test/gfx/warn_group_output.png differ