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;
diff --git a/src/task.c b/src/task.c
index 11255c3..e169201 100644
--- a/src/task.c
+++ b/src/task.c
@@ -33,7 +33,7 @@
 struct pool_head *pool_head_notification;
 
 unsigned int nb_tasks = 0;
-unsigned long active_tasks_mask = 0; /* Mask of threads with active tasks */
+volatile unsigned long active_tasks_mask = 0; /* Mask of threads with active tasks */
 unsigned long global_tasks_mask = 0; /* Mask of threads with tasks in the global runqueue */
 unsigned int tasks_run_queue = 0;
 unsigned int tasks_run_queue_cur = 0;    /* copy of the run queue size */