diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 18f7eab5d..14385a12b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -124,6 +124,7 @@ static void tests() {
  */
 int main() {
     tests(); // run self-test implementations
+    return 0;
 }
 ```