diff --git a/Modules/main.c b/Modules/main.c
index dc46d550c6e..7594a762e02 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -183,7 +183,7 @@ static int RunModule(char *module)
    "threading" threads have completed. */
 #include "abstract.h"
 static void
-WaitForThreadShutdown()
+WaitForThreadShutdown(void)
 {
 #ifdef WITH_THREAD
 	PyObject *result;