diff --git a/IPython/core/extensions.py b/IPython/core/extensions.py
index 5c05d46..87c6711 100644
--- a/IPython/core/extensions.py
+++ b/IPython/core/extensions.py
@@ -49,8 +49,7 @@ class ExtensionManager(Configurable):
     is added to ``sys.path`` automatically.
     """
 
-    shell = Instance('IPython.core.interactiveshell.InteractiveShellABC').tag(
-                     allow_none=True)
+    shell = Instance('IPython.core.interactiveshell.InteractiveShellABC', allow_none=True)
 
     def __init__(self, shell=None, **kwargs):
         super(ExtensionManager, self).__init__(shell=shell, **kwargs)