diff --git a/Python/thread.c b/Python/thread.c
index c8b2809f62..0f4c392b2d 100644
--- a/Python/thread.c
+++ b/Python/thread.c
@@ -85,7 +85,7 @@ static int thread_debug = 0;
 
 static int initialized;
 
-static void PyThread__init_thread(); /* Forward */
+static void PyThread__init_thread(void); /* Forward */
 
 void PyThread_init_thread(void)
 {