diff --git a/IPython/Shell.py b/IPython/Shell.py
index 910ea70..1e91d54 100644
--- a/IPython/Shell.py
+++ b/IPython/Shell.py
@@ -46,6 +46,13 @@ from IPython.ipmaker import make_IPython
 from IPython.Magic import Magic
 from IPython.ipstruct import Struct
 
+try: # Python 2.3 compatibility
+    set
+except NameError:
+    import sets
+    set = sets.Set
+
+
 # Globals
 # global flag to pass around information about Ctrl-C without exceptions
 KBINT = False