diff --git a/include/proto/task.h b/include/proto/task.h
index fe4699a..cb3f9af 100644
--- a/include/proto/task.h
+++ b/include/proto/task.h
@@ -83,7 +83,7 @@
 
 /* a few exported variables */
 extern unsigned int nb_tasks;     /* total number of tasks */
-extern unsigned long active_tasks_mask; /* Mask of threads with active tasks */
+extern volatile unsigned long active_tasks_mask; /* Mask of threads with active tasks */
 extern unsigned int tasks_run_queue;    /* run queue size */
 extern unsigned int tasks_run_queue_cur;
 extern unsigned int nb_tasks_cur;