diff --git a/tests-clar/diff/patch.c b/tests-clar/diff/patch.c
index 3da9ce82b..fdb79a475 100644
--- a/tests-clar/diff/patch.c
+++ b/tests-clar/diff/patch.c
@@ -30,6 +30,7 @@ static int check_removal_cb(
 	size_t output_len)
 {
 	GIT_UNUSED(cb_data);
+	GIT_UNUSED(output_len);
 
 	switch (line_origin) {
 	case GIT_DIFF_LINE_FILE_HDR: