diff --git a/src/timer/SDL_timer.c b/src/timer/SDL_timer.c
index 353b19fd7..2c98431ac 100644
--- a/src/timer/SDL_timer.c
+++ b/src/timer/SDL_timer.c
@@ -95,6 +95,7 @@ void SDL_TimerQuit(void)
 	}
 	if ( SDL_timer_threaded ) {
 		SDL_DestroyMutex(SDL_timer_mutex);
+		SDL_timer_mutex = NULL;
 	}
 	SDL_timer_started = 0;
 	SDL_timer_threaded = 0;