diff --git a/include/extern/utf8decoder.hpp b/include/extern/utf8decoder.hpp
index 64a9a187..82ab84f1 100644
--- a/include/extern/utf8decoder.hpp
+++ b/include/extern/utf8decoder.hpp
@@ -8,6 +8,11 @@
 #define UTF8_ACCEPT 0
 #define UTF8_REJECT 12
 
-uint32_t decode(uint32_t *state, uint32_t *codep, uint8_t byte);
+struct Utf8Decoder {
+	uint32_t state = UTF8_ACCEPT;
+	uint32_t codepoint = 0;
+
+	uint32_t update(uint8_t byte);
+};
 
 #endif // RGBDS_EXTERN_UTF8DECODER_HPP
diff --git a/src/asm/actions.cpp b/src/asm/actions.cpp
index c4a758ba..75440926 100644
--- a/src/asm/actions.cpp
+++ b/src/asm/actions.cpp
@@ -279,18 +279,17 @@ static void errorInvalidUTF8Byte(uint8_t byte, char const *functionName) {
 
 size_t act_StringLen(std::string const &str, bool printErrors) {
 	size_t len = 0;
-	uint32_t state = UTF8_ACCEPT;
-	uint32_t codepoint = 0;
+	Utf8Decoder decoder;
 
 	for (char c : str) {
 		uint8_t byte = static_cast<uint8_t>(c);
 
-		switch (decode(&state, &codepoint, byte)) {
+		switch (decoder.update(byte)) {
 		case UTF8_REJECT:
 			if (printErrors) {
 				errorInvalidUTF8Byte(byte, "STRLEN");
 			}
-			state = UTF8_ACCEPT;
+			decoder.state = UTF8_ACCEPT;
 			// fallthrough
 		case UTF8_ACCEPT:
 			++len;
@@ -299,7 +298,7 @@ size_t act_StringLen(std::string const &str, bool printErrors) {
 	}
 
 	// Check for partial code point.
-	if (state != UTF8_ACCEPT) {
+	if (decoder.state != UTF8_ACCEPT) {
 		if (printErrors) {
 			error("STRLEN: Incomplete UTF-8 character");
 		}
@@ -317,16 +316,15 @@ std::string
 
 	size_t strLen = str.length();
 	size_t index = 0;
-	uint32_t state = UTF8_ACCEPT;
-	uint32_t codepoint = 0;
+	Utf8Decoder decoder;
 	uint32_t curIdx = 0;
 
 	// Advance to starting index in source string.
 	while (index < strLen && curIdx < start) {
-		switch (decode(&state, &codepoint, str[index])) {
+		switch (decoder.update(str[index])) {
 		case UTF8_REJECT:
 			errorInvalidUTF8Byte(str[index], "STRSLICE");
-			state = UTF8_ACCEPT;
+			decoder.state = UTF8_ACCEPT;
 			// fallthrough
 		case UTF8_ACCEPT:
 			++curIdx;
@@ -349,10 +347,10 @@ std::string
 
 	// Advance to ending index in source string.
 	while (index < strLen && curIdx < stop) {
-		switch (decode(&state, &codepoint, str[index])) {
+		switch (decoder.update(str[index])) {
 		case UTF8_REJECT:
 			errorInvalidUTF8Byte(str[index], "STRSLICE");
-			state = UTF8_ACCEPT;
+			decoder.state = UTF8_ACCEPT;
 			// fallthrough
 		case UTF8_ACCEPT:
 			++curIdx;
@@ -362,7 +360,7 @@ std::string
 	}
 
 	// Check for partial code point.
-	if (state != UTF8_ACCEPT) {
+	if (decoder.state != UTF8_ACCEPT) {
 		error("STRSLICE: Incomplete UTF-8 character");
 		++curIdx;
 	}
@@ -387,16 +385,15 @@ std::string act_StringSub(std::string const &str, int32_t negPos, std::optional<
 
 	size_t strLen = str.length();
 	size_t index = 0;
-	uint32_t state = UTF8_ACCEPT;
-	uint32_t codepoint = 0;
+	Utf8Decoder decoder;
 	uint32_t curPos = 1;
 
 	// Advance to starting position in source string.
 	while (index < strLen && curPos < pos) {
-		switch (decode(&state, &codepoint, str[index])) {
+		switch (decoder.update(str[index])) {
 		case UTF8_REJECT:
 			errorInvalidUTF8Byte(str[index], "STRSUB");
-			state = UTF8_ACCEPT;
+			decoder.state = UTF8_ACCEPT;
 			// fallthrough
 		case UTF8_ACCEPT:
 			++curPos;
@@ -418,10 +415,10 @@ std::string act_StringSub(std::string const &str, int32_t negPos, std::optional<
 
 	// Compute the result length in bytes.
 	while (index < strLen && curLen < len) {
-		switch (decode(&state, &codepoint, str[index])) {
+		switch (decoder.update(str[index])) {
 		case UTF8_REJECT:
 			errorInvalidUTF8Byte(str[index], "STRSUB");
-			state = UTF8_ACCEPT;
+			decoder.state = UTF8_ACCEPT;
 			// fallthrough
 		case UTF8_ACCEPT:
 			++curLen;
@@ -431,7 +428,7 @@ std::string act_StringSub(std::string const &str, int32_t negPos, std::optional<
 	}
 
 	// Check for partial code point.
-	if (state != UTF8_ACCEPT) {
+	if (decoder.state != UTF8_ACCEPT) {
 		error("STRSUB: Incomplete UTF-8 character");
 		++curLen;
 	}
diff --git a/src/asm/charmap.cpp b/src/asm/charmap.cpp
index 6e000ad4..473a31fe 100644
--- a/src/asm/charmap.cpp
+++ b/src/asm/charmap.cpp
@@ -273,15 +273,14 @@ size_t charmap_ConvertNext(std::string_view &input, std::vector<int32_t> *output
 	} else if (inputIdx < input.length()) { // No match found, but there is some input left
 		size_t codepointLen = 0;
 		// This will write the codepoint's value to `output`, little-endian
-		for (uint32_t state = UTF8_ACCEPT, codepoint = 0;
-		     inputIdx + codepointLen < input.length();) {
-			if (decode(&state, &codepoint, input[inputIdx + codepointLen]) == UTF8_REJECT) {
+		for (Utf8Decoder decoder; inputIdx + codepointLen < input.length();) {
+			if (decoder.update(input[inputIdx + codepointLen]) == UTF8_REJECT) {
 				error("Input string is not valid UTF-8");
 				codepointLen = 1;
 				break;
 			}
 			++codepointLen;
-			if (state == UTF8_ACCEPT) {
+			if (decoder.state == UTF8_ACCEPT) {
 				break;
 			}
 		}
diff --git a/src/extern/utf8decoder.cpp b/src/extern/utf8decoder.cpp
index 3f9505f0..1cc60dfe 100644
--- a/src/extern/utf8decoder.cpp
+++ b/src/extern/utf8decoder.cpp
@@ -42,9 +42,9 @@ static uint8_t const utf8d[] = {
 };
 // clang-format on
 
-uint32_t decode(uint32_t *state, uint32_t *codep, uint8_t byte) {
+uint32_t Utf8Decoder::update(uint8_t byte) {
 	uint8_t type = utf8d[byte];
-	*codep = *state != UTF8_ACCEPT ? (byte & 0b111111) | (*codep << 6) : (0xff >> type) & byte;
-	*state = utf8d[0x100 + *state + type];
-	return *state;
+	codepoint = state != UTF8_ACCEPT ? (byte & 0b111111) | (codepoint << 6) : (0xff >> type) & byte;
+	state = utf8d[0x100 + state + type];
+	return state;
 }
diff --git a/src/link/output.cpp b/src/link/output.cpp
index 8d9db7ad..3a6f417e 100644
--- a/src/link/output.cpp
+++ b/src/link/output.cpp
@@ -275,23 +275,24 @@ static void writeSymName(std::string const &name, FILE *file) {
 
 		// Output illegal characters using Unicode escapes ('\u' or '\U')
 		// Decode the UTF-8 codepoint; or at least attempt to
-		uint32_t state = UTF8_ACCEPT, codepoint;
+		Utf8Decoder decoder;
 		do {
-			decode(&state, &codepoint, *ptr);
-			if (state != UTF8_REJECT) {
+			if (decoder.update(*ptr) != UTF8_REJECT) {
 				++ptr;
 				continue;
 			}
 			// This sequence was invalid; emit a U+FFFD, and recover
-			codepoint = 0xFFFD;
+			decoder.codepoint = 0xFFFD;
 			// Skip continuation bytes
 			// A NUL byte does not qualify, so we're good
 			while ((*ptr & 0xC0) == 0x80) {
 				++ptr;
 			}
 			break;
-		} while (state != UTF8_ACCEPT);
-		fprintf(file, codepoint <= 0xFFFF ? "\\u%04" PRIx32 : "\\U%08" PRIx32, codepoint);
+		} while (decoder.state != UTF8_ACCEPT);
+		fprintf(
+		    file, decoder.codepoint <= 0xFFFF ? "\\u%04" PRIx32 : "\\U%08" PRIx32, decoder.codepoint
+		);
 	}
 }