Index: core/handlers/base.py
===================================================================
--- core/handlers/base.py	(revision 1289)
+++ core/handlers/base.py	(working copy)
@@ -17,9 +17,12 @@
         self._response_middleware = []
         self._exception_middleware = []
         for middleware_path in settings.MIDDLEWARE_CLASSES:
-            dot = middleware_path.rindex('.')
-            mw_module, mw_classname = middleware_path[:dot], middleware_path[dot+1:]
             try:
+                dot = middleware_path.rindex('.')
+                mw_module, mw_classname = middleware_path[:dot], middleware_path[dot+1:]
+            except ValueError:
+                raise exceptions.ImproperlyConfigured, '"%s" does not look like a middleware module' % (middleware_path)
+            try:
                 mod = __import__(mw_module, '', '', [''])
             except ImportError, e:
                 raise exceptions.ImproperlyConfigured, 'Error importing middleware %s: "%s"' % (mw_module, e)