diff --git a/spyder_kernels/comms/frontendcomm.py b/spyder_kernels/comms/frontendcomm.py
index f23fa196..637a188e 100644
--- a/spyder_kernels/comms/frontendcomm.py
+++ b/spyder_kernels/comms/frontendcomm.py
@@ -128,10 +128,11 @@ def _check_comm_reply(self):
         """
         Send comm message to frontend to check if the iopub channel is ready
         """
-        if len(self._pending_comms) == 0:
-            return
-        for comm in self._pending_comms.values():
-            self._notify_comm_ready(comm)
+        with self.comm_lock:
+            if len(self._pending_comms) == 0:
+                return
+            for comm in self._pending_comms.values():
+                self._notify_comm_ready(comm)
         self.kernel.io_loop.call_later(1, self._check_comm_reply)
 
     def _notify_comm_ready(self, comm):
@@ -143,7 +144,8 @@ def _notify_comm_ready(self, comm):
 
     def _comm_ready_callback(self, ret):
         """A comm has replied, so process all cached messages related to it."""
-        comm = self._pending_comms.pop(self.calling_comm_id, None)
+        with self.comm_lock:
+            comm = self._pending_comms.pop(self.calling_comm_id, None)
         if not comm:
             return
         # Cached messages for that comm
@@ -177,7 +179,8 @@ def _comm_open(self, comm, msg):
 
         # IOPub might not be connected yet, keep sending messages until a
         # reply is received.
-        self._pending_comms[comm.comm_id] = comm
+        with self.comm_lock:
+            self._pending_comms[comm.comm_id] = comm
         self._notify_comm_ready(comm)
         self.kernel.io_loop.call_later(.3, self._check_comm_reply)