diff --git a/uisimulator/sdl/thread-sdl.c b/uisimulator/sdl/thread-sdl.c
index 1522f318a6..ef7c86c3b4 100644
--- a/uisimulator/sdl/thread-sdl.c
+++ b/uisimulator/sdl/thread-sdl.c
@@ -57,7 +57,7 @@ struct thread_entry threads[MAXTHREADS];
  * way to get them back in there so they may exit */
 static jmp_buf thread_jmpbufs[MAXTHREADS];
 static SDL_mutex *m;
-static bool threads_exit = false;
+static volatile bool threads_exit = false;
 
 extern long start_tick;