diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 5c4ceca..274f988 100644
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -260,7 +260,7 @@
 int  thread_no_sync(void);
 int  thread_need_sync(void);
 
-extern unsigned long all_threads_mask;
+extern volatile unsigned long all_threads_mask;
 
 #define ha_sigmask(how, set, oldset)  pthread_sigmask(how, set, oldset)