diff --git a/src/asm/output.cpp b/src/asm/output.cpp
index 70a251c29..b0a4e040f 100644
--- a/src/asm/output.cpp
+++ b/src/asm/output.cpp
@@ -492,7 +492,7 @@ static bool dumpMacros(FILE *file) {
 void out_WriteState(std::string name, std::vector<StateFeature> const &features) {
 	FILE *file;
 	if (name != "-") {
-		file = fopen(name.c_str(), "w");
+		file = fopen(name.c_str(), "wb");
 	} else {
 		name = "<stdout>";
 		file = fdopen(STDOUT_FILENO, "w");
diff --git a/test/asm/test.sh b/test/asm/test.sh
index c175ebdec..2209fe7cf 100755
--- a/test/asm/test.sh
+++ b/test/asm/test.sh
@@ -5,11 +5,23 @@ export LC_ALL=C
 # Game Boy release date, 1989-04-21T12:34:56Z (for reproducible test results)
 export SOURCE_DATE_EPOCH=609165296
 
-o="$(mktemp)"
-gb="$(mktemp)"
-input="$(mktemp)"
-output="$(mktemp)"
-errput="$(mktemp)"
+# On Windows, the paths returned by `mktemp` are Unix paths, whereas RGBDS expects Windows paths.
+# Bash implicitly translates them when recognised, but this breaks if the path is prefixed
+# (at-files, state file spec, etc.); thus, return an absolute path instead.
+set -x
+	unix_path=$(mktemp)
+	realpath "$unix_path"
+	echo "$unix_path"
+	printf '%s\n' "$unix_path"
+	echo.exe "$unix_path"
+	cygpath "$unix_path"
+set +x
+
+o="$(make_temp_file)"
+gb="$(make_temp_file)"
+input="$(make_temp_file)"
+output="$(make_temp_file)"
+errput="$(make_temp_file)"
 
 # Immediate expansion is the desired behavior.
 # shellcheck disable=SC2064