diff --git a/tests/base64_test.h b/tests/base64_test.h
index 9e44d6f..0e25543 100644
--- a/tests/base64_test.h
+++ b/tests/base64_test.h
@@ -1,2 +1,4 @@
-void test_base64_encode_good();
-void test_base64_decode_good();
+#ifndef BASE64_TEST_H
+void test_base64_encode_good(void);
+void test_base64_decode_good(void);
+#endif