diff --git a/kombu/transport/sqlalchemy/__init__.py b/kombu/transport/sqlalchemy/__init__.py
index bcf9ed5b..fe469fae 100644
--- a/kombu/transport/sqlalchemy/__init__.py
+++ b/kombu/transport/sqlalchemy/__init__.py
@@ -4,6 +4,7 @@
 
 from __future__ import absolute_import, unicode_literals
 
+import threading
 from json import loads, dumps
 
 from sqlalchemy import create_engine
@@ -21,6 +22,8 @@ from .models import (ModelBase, Queue as QueueBase, Message as MessageBase,
 VERSION = (1, 1, 0)
 __version__ = '.'.join(map(str, VERSION))
 
+_MUTEX = threading.Lock()
+
 
 class Channel(virtual.Channel):
     """The channel class."""
@@ -127,9 +130,10 @@ class Channel(virtual.Channel):
         return self._query_all(queue).count()
 
     def _declarative_cls(self, name, base, ns):
-        if name in class_registry:
-            return class_registry[name]
-        return type(str(name), (base, ModelBase), ns)
+        with _MUTEX:
+            if name in class_registry:
+                return class_registry[name]
+            return type(str(name), (base, ModelBase), ns)
 
     @cached_property
     def queue_cls(self):