diff --git a/src/fix/main.cpp b/src/fix/main.cpp
index 7c760e50..f11d2d62 100644
--- a/src/fix/main.cpp
+++ b/src/fix/main.cpp
@@ -92,14 +92,10 @@ static Usage usage = {
 // clang-format on
 
 static void parseByte(uint16_t &output, char name) {
-	if (musl_optarg[0] == '\0') {
-		fatal("Argument to option '-%c' may not be empty", name);
-	}
-
 	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: %" PRIu64, name, *value);
+		fatal("Invalid argument for option '-%c'", name);
+	} else if (*value > 0xFF) {
+		fatal("Argument for option '-%c' must be between 0 and 0xFF", name);
 	} else {
 		output = *value;
 	}
@@ -117,9 +113,11 @@ static void initLogo() {
 		if (strcmp(options.logoFilename, "-")) {
 			logoFile = fopen(options.logoFilename, "rb");
 		} else {
+			// LCOV_EXCL_START
 			options.logoFilename = "<stdin>";
 			(void)setmode(STDIN_FILENO, O_BINARY);
 			logoFile = stdin;
+			// LCOV_EXCL_STOP
 		}
 		if (!logoFile) {
 			// LCOV_EXCL_START
diff --git a/test/fix/bad-custom-logo.1bpp b/test/fix/bad-custom-logo.1bpp
new file mode 100644
index 00000000..1b1cb4d4
Binary files /dev/null and b/test/fix/bad-custom-logo.1bpp differ
diff --git a/test/fix/bad-custom-logo.err b/test/fix/bad-custom-logo.err
new file mode 100644
index 00000000..05615c86
--- /dev/null
+++ b/test/fix/bad-custom-logo.err
@@ -0,0 +1 @@
+FATAL: "bad-custom-logo.1bpp" is not 48 bytes
diff --git a/test/fix/bad-custom-logo.flags b/test/fix/bad-custom-logo.flags
new file mode 100644
index 00000000..2cb3a012
--- /dev/null
+++ b/test/fix/bad-custom-logo.flags
@@ -0,0 +1 @@
+-L ./bad-custom-logo.1bpp
diff --git a/test/fix/deprecated-overwrite.bin b/test/fix/deprecated-overwrite.bin
new file mode 100644
index 00000000..512fb85a
Binary files /dev/null and b/test/fix/deprecated-overwrite.bin differ
diff --git a/test/fix/deprecated-overwrite.err b/test/fix/deprecated-overwrite.err
new file mode 100644
index 00000000..5cdef849
--- /dev/null
+++ b/test/fix/deprecated-overwrite.err
@@ -0,0 +1 @@
+warning: '-O' is deprecated; use '-Wno-overwrite' instead [-Wobsolete]
diff --git a/test/fix/deprecated-overwrite.flags b/test/fix/deprecated-overwrite.flags
new file mode 100644
index 00000000..bc6ebd5e
--- /dev/null
+++ b/test/fix/deprecated-overwrite.flags
@@ -0,0 +1 @@
+-O -v
diff --git a/test/fix/deprecated-overwrite.gb b/test/fix/deprecated-overwrite.gb
new file mode 100644
index 00000000..53188fd2
Binary files /dev/null and b/test/fix/deprecated-overwrite.gb differ
diff --git a/test/fix/disable-warnings.bin b/test/fix/disable-warnings.bin
new file mode 100644
index 00000000..ab24776d
Binary files /dev/null and b/test/fix/disable-warnings.bin differ
diff --git a/test/fix/disable-warnings.flags b/test/fix/disable-warnings.flags
new file mode 100644
index 00000000..78739d7e
--- /dev/null
+++ b/test/fix/disable-warnings.flags
@@ -0,0 +1,2 @@
+-w -m mbc3+ram -r 0
+The "-w" suppresses "-Wmbc" and "-Woverwrite" warnings
diff --git a/test/fix/disable-warnings.gb b/test/fix/disable-warnings.gb
new file mode 100644
index 00000000..ac86ca57
Binary files /dev/null and b/test/fix/disable-warnings.gb differ
diff --git a/test/fix/invalid-color.err b/test/fix/invalid-color.err
new file mode 100644
index 00000000..1a404429
--- /dev/null
+++ b/test/fix/invalid-color.err
@@ -0,0 +1 @@
+FATAL: Invalid argument for option '--color'
diff --git a/test/fix/invalid-color.flags b/test/fix/invalid-color.flags
new file mode 100644
index 00000000..a69ba475
--- /dev/null
+++ b/test/fix/invalid-color.flags
@@ -0,0 +1 @@
+--color=chartreuse
diff --git a/test/fix/invalid-numeric-arg.err b/test/fix/invalid-numeric-arg.err
new file mode 100644
index 00000000..afe82baa
--- /dev/null
+++ b/test/fix/invalid-numeric-arg.err
@@ -0,0 +1 @@
+FATAL: Invalid argument for option '-r'
diff --git a/test/fix/invalid-numeric-arg.flags b/test/fix/invalid-numeric-arg.flags
new file mode 100644
index 00000000..a11267b1
--- /dev/null
+++ b/test/fix/invalid-numeric-arg.flags
@@ -0,0 +1 @@
+-r invalid
diff --git a/test/fix/invalid-numeric-range.err b/test/fix/invalid-numeric-range.err
new file mode 100644
index 00000000..5debeb24
--- /dev/null
+++ b/test/fix/invalid-numeric-range.err
@@ -0,0 +1 @@
+FATAL: Argument for option '-r' must be between 0 and 0xFF
diff --git a/test/fix/invalid-numeric-range.flags b/test/fix/invalid-numeric-range.flags
new file mode 100644
index 00000000..1e090731
--- /dev/null
+++ b/test/fix/invalid-numeric-range.flags
@@ -0,0 +1 @@
+-r 999
diff --git a/test/fix/multiple-to-one.err b/test/fix/multiple-to-one.err
new file mode 100644
index 00000000..1831bee3
--- /dev/null
+++ b/test/fix/multiple-to-one.err
@@ -0,0 +1,17 @@
+FATAL: If '-o' is set then only a single input file may be specified
+Usage: rgbfix [-hjOsVvw] [-C | -c] [-f <fix_spec>] [-i <game_id>]
+              [-k <licensee>] [-L <logo_file>] [-l <licensee_byte>]
+              [-m <mbc_type>] [-n <rom_version>] [-p <pad_value>]
+              [-r <ram_size>] [-t <title_str>] [-W warning] <file> ...
+
+Useful options:
+    -m, --mbc-type <value>   set the MBC type byte to this value; "-m help"
+                             or "-m list" prints the accepted values
+    -p, --pad-value <value>  pad to the next valid size using this value
+    -r, --ram-size <code>    set the cart RAM size byte to this value
+    -o, --output <path>      set the output file
+    -V, --version            print RGBFIX version and exit
+    -v, --validate           fix the header logo and both checksums ("-f lhg")
+    -W, --warning <warning>  enable or disable warnings
+
+For more help, use "man rgbfix" or go to https://rgbds.gbdev.io/docs/
diff --git a/test/fix/no-exist.err b/test/fix/no-exist.err
new file mode 100644
index 00000000..2a70e7a5
--- /dev/null
+++ b/test/fix/no-exist.err
@@ -0,0 +1,2 @@
+error: Failed to open "no-exist" for reading+writing: No such file or directory
+Fixing "no-exist" failed with 1 error
diff --git a/test/fix/no-input.err b/test/fix/no-input.err
new file mode 100644
index 00000000..6f31f6da
--- /dev/null
+++ b/test/fix/no-input.err
@@ -0,0 +1,17 @@
+FATAL: No input file specified (pass "-" to read from standard input)
+Usage: rgbfix [-hjOsVvw] [-C | -c] [-f <fix_spec>] [-i <game_id>]
+              [-k <licensee>] [-L <logo_file>] [-l <licensee_byte>]
+              [-m <mbc_type>] [-n <rom_version>] [-p <pad_value>]
+              [-r <ram_size>] [-t <title_str>] [-W warning] <file> ...
+
+Useful options:
+    -m, --mbc-type <value>   set the MBC type byte to this value; "-m help"
+                             or "-m list" prints the accepted values
+    -p, --pad-value <value>  pad to the next valid size using this value
+    -r, --ram-size <code>    set the cart RAM size byte to this value
+    -o, --output <path>      set the output file
+    -V, --version            print RGBFIX version and exit
+    -v, --validate           fix the header logo and both checksums ("-f lhg")
+    -W, --warning <warning>  enable or disable warnings
+
+For more help, use "man rgbfix" or go to https://rgbds.gbdev.io/docs/
diff --git a/test/fix/noexist.err b/test/fix/noexist.err
deleted file mode 100644
index c4940146..00000000
--- a/test/fix/noexist.err
+++ /dev/null
@@ -1,2 +0,0 @@
-error: Failed to open "noexist" for reading+writing: No such file or directory
-Fixing "noexist" failed with 1 error
diff --git a/test/fix/ramful-mbc-2-kb.err b/test/fix/ramful-mbc-2-kb.err
new file mode 100644
index 00000000..89d4b45f
--- /dev/null
+++ b/test/fix/ramful-mbc-2-kb.err
@@ -0,0 +1 @@
+warning: RAM size 1 (2 KiB) was specified for MBC "MBC1+RAM" [-Wmbc]
diff --git a/test/fix/ramful-mbc-2-kb.flags b/test/fix/ramful-mbc-2-kb.flags
new file mode 100644
index 00000000..633469c0
--- /dev/null
+++ b/test/fix/ramful-mbc-2-kb.flags
@@ -0,0 +1 @@
+-m mbc1+ram -r 1
diff --git a/test/fix/ramful-mbc-2-kb.gb b/test/fix/ramful-mbc-2-kb.gb
new file mode 100644
index 00000000..b049171e
Binary files /dev/null and b/test/fix/ramful-mbc-2-kb.gb differ
diff --git a/test/fix/rom-ram-not-2-kb.err b/test/fix/rom-ram-not-2-kb.err
new file mode 100644
index 00000000..19029e4e
--- /dev/null
+++ b/test/fix/rom-ram-not-2-kb.err
@@ -0,0 +1,2 @@
+warning: MBC "rom+ram" is under-specified and poorly supported [-Wmbc]
+warning: MBC "ROM+RAM" should have 2 KiB of RAM ("-r 1") [-Wmbc]
diff --git a/test/fix/rom-ram-not-2-kb.flags b/test/fix/rom-ram-not-2-kb.flags
new file mode 100644
index 00000000..32834b1f
--- /dev/null
+++ b/test/fix/rom-ram-not-2-kb.flags
@@ -0,0 +1 @@
+-m rom+ram -r 2
diff --git a/test/fix/rom-ram-not-2-kb.gb b/test/fix/rom-ram-not-2-kb.gb
new file mode 100644
index 00000000..35368a30
Binary files /dev/null and b/test/fix/rom-ram-not-2-kb.gb differ
diff --git a/test/fix/test.sh b/test/fix/test.sh
index 46e2586d..550a5beb 100755
--- a/test/fix/test.sh
+++ b/test/fix/test.sh
@@ -12,6 +12,16 @@ cd "$tmpdir" || exit
 # shellcheck disable=SC2064
 trap "cd; rm -rf ${tmpdir@Q}" EXIT
 
+if which cygpath &>/dev/null; then
+	# MinGW needs the Windows path substituted but with forward slash separators;
+	# Cygwin has `cygpath` but just needs the original path substituted.
+	subst1="$(printf '%s\n' "$src" | sed 's:[][\/.^$*]:\\&:g')"
+	subst2="$(printf '%s\n' "$(cygpath -w "$src")" | sed -e 's:\\:/:g' -e 's:[][\/.^$*]:\\&:g')"
+	src_subst="$src/\\|$subst1/\\|$subst2/"
+else
+	src_subst="$src/"
+fi
+
 tests=0
 failed=0
 rc=0
@@ -83,9 +93,9 @@ runTest () {
 		else
 			desired_errname=/dev/null
 		fi
-		sed "s/$subst/<filename>/g" out.out | tryDiff "$desired_outname" - "$1.out${variant}"
+		sed -e "s/$subst/<filename>/g" -e "s#$src_subst##g" out.out | tryDiff "$desired_outname" - "$1.out${variant}"
 		(( our_rc = our_rc || $? ))
-		sed "s/$subst/<filename>/g" out.err | tryDiff "$desired_errname" - "$1.err${variant}"
+		sed -e "s/$subst/<filename>/g" -e "s#$src_subst##g" out.err | tryDiff "$desired_errname" - "$1.err${variant}"
 		(( our_rc = our_rc || $? ))
 
 		if [[ -r "$2/$1.gb" ]]; then
@@ -101,6 +111,16 @@ runTest () {
 	done
 }
 
+runSpecialTest () {
+	name="$1"
+	shift
+	echo "${bold}${green}${name}...${rescolors}${resbold}"
+	eval "$RGBFIX" "$@" '2>out.err'
+	rc=$((rc || $? != 1))
+	tryDiff "$src/${name}.err" out.err "${name}.err"
+	rc=$((rc || $?))
+}
+
 rm -f padding*_* # Delete padding test cases generated but not deleted (e.g. interrupted)
 
 progress=1
@@ -108,6 +128,15 @@ for i in "$src"/*.flags; do
 	runTest "$(basename "$i" .flags)" "$src"
 done
 
+# Check that RGBFIX errors out when inputting a non-existent file
+runSpecialTest no-exist no-exist
+
+# Check that RGBFIX errors out when not inputting any file
+runSpecialTest no-input
+
+# Check that RGBFIX errors out when inputting multiple files with an output file
+runSpecialTest multiple-to-one one two three -o multiple-to-one
+
 # Check the result with all different padding bytes
 echo "${bold}Checking padding...${resbold}"
 cp "$src"/padding{,-large,-larger}.bin .
@@ -124,12 +153,6 @@ for (( i=0; i < 10; ++i )); do
 done
 echo "${bold}Done checking padding!${resbold}"
 
-# Check that RGBFIX errors out when inputting a non-existent file...
-$RGBFIX noexist 2>out.err
-rc=$((rc || $? != 1))
-tryDiff "$src/noexist.err" out.err noexist.err
-rc=$((rc || $?))
-
 if [[ "$failed" -eq 0 ]]; then
 	echo "${bold}${green}All ${tests} tests passed!${rescolors}${resbold}"
 else