diff --git a/t/test-lib.sh b/t/test-lib.sh
index d9988503..ee931398 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1230,7 +1230,7 @@ case $uname_s in
 	test_set_prereq SED_STRIPS_CR
 	test_set_prereq GREP_STRIPS_CR
 	test_set_prereq WINDOWS
-	GIT_TEST_CMP="GIT_DIR=/dev/null git diff --no-index --ignore-cr-at-eol --"
+	GIT_TEST_CMP=mingw_test_cmp
 	;;
 *CYGWIN*)
 	test_set_prereq POSIXPERM