diff --git a/IPython/core/formatters.py b/IPython/core/formatters.py
index e7c01ba..689e5be 100644
--- a/IPython/core/formatters.py
+++ b/IPython/core/formatters.py
@@ -26,6 +26,7 @@ Authors:
 # Stdlib imports
 import abc
 import sys
+import warnings
 # We must use StringIO, as cStringIO doesn't handle unicode properly.
 from StringIO import StringIO