diff --git a/src/common/WorkQueue.h b/src/common/WorkQueue.h
index 300ae7d7d71800..ef6991b4569d73 100644
--- a/src/common/WorkQueue.h
+++ b/src/common/WorkQueue.h
@@ -340,10 +340,12 @@ class ThreadPool : public md_config_obs_t {
   
   /// assign a work queue to this thread pool
   void add_work_queue(WorkQueue_* wq) {
+    Mutex::Locker l(_lock);
     work_queues.push_back(wq);
   }
   /// remove a work queue from this thread pool
   void remove_work_queue(WorkQueue_* wq) {
+    Mutex::Locker l(_lock);
     unsigned i = 0;
     while (work_queues[i] != wq)
       i++;