diff --git a/src/msg/async/rdma/RDMAStack.cc b/src/msg/async/rdma/RDMAStack.cc
index dcc6e1a8fb3db..7e5c9d3e9bf37 100644
--- a/src/msg/async/rdma/RDMAStack.cc
+++ b/src/msg/async/rdma/RDMAStack.cc
@@ -99,8 +99,11 @@ void RDMADispatcher::polling_start()
 
 void RDMADispatcher::polling_stop()
 {
-  Mutex::Locker l(lock);
-  done = true;
+  {
+    Mutex::Locker l(lock);
+    done = true;
+  }
+
   if (!t.joinable())
     return;