diff --git a/ext/gd/config.m4 b/ext/gd/config.m4
index b342074027059..826d7c7c826a2 100644
--- a/ext/gd/config.m4
+++ b/ext/gd/config.m4
@@ -194,7 +194,7 @@ dnl Various checks for GD features
 
     PHP_TEST_BUILD(foobar, [], [
       AC_MSG_ERROR([GD build test failed. Please check the config.log for details.])
-    ], [ $GD_SHARED_LIBADD ], [char foobar () {}])
+    ], [ $GD_SHARED_LIBADD ], [char foobar(void) { return '\0'; }])
 
   else
     extra_sources="gd_compat.c"