diff --git a/observer.py b/observer.py
index 46d10c8..c25efa6 100644
--- a/observer.py
+++ b/observer.py
@@ -11,9 +11,10 @@ class Observer:
             self.__receivers_list[identifier].add(queue)
             return Subscription(self, identifier, queue)
     def publish(self, identifier, message):
-        if identifier in self.__receivers_list:
-            for queue in self.__receivers_list[identifier]:
-                queue.put(message)
+        with self.__lock:
+            if identifier in self.__receivers_list:
+                for queue in self.__receivers_list[identifier]:
+                    queue.put(message)
     def quit(self, identifer, queue):
         with self.__lock:
             self.__receivers_list[identifer].remove(queue)