diff --git a/ffserver.c b/ffserver.c
index d2bdcc328e..1fc3e656c2 100644
--- a/ffserver.c
+++ b/ffserver.c
@@ -4441,7 +4441,7 @@ static void handle_child_exit(int sig)
     need_to_start_children = 1;
 }
 
-static void opt_debug()
+static void opt_debug(void)
 {
     ffserver_debug = 1;
     ffserver_daemon = 0;