diff --git a/test/metal-test.h b/test/metal-test.h
index e1a18ac9..495b561b 100644
--- a/test/metal-test.h
+++ b/test/metal-test.h
@@ -33,7 +33,8 @@ extern void metal_add_test_case(struct metal_test_case *test_case);
 
 
 #define METAL_ADD_TEST(func)						\
-__attribute__ ((constructor)) static void metal_test_##func() {		\
+__attribute__ ((constructor)) static void metal_test_##func(void)	\
+{									\
 	static struct metal_test_case metal_test_##func = {		\
 		.name	= #func,					\
 		.test	= func,						\