diff --git a/django/core/handlers/base.py b/django/core/handlers/base.py
index ba2e286721..c34d0b52cb 100644
--- a/django/core/handlers/base.py
+++ b/django/core/handlers/base.py
@@ -17,7 +17,10 @@ class BaseHandler:
         self._response_middleware = []
         self._exception_middleware = []
         for middleware_path in settings.MIDDLEWARE_CLASSES:
-            dot = middleware_path.rindex('.')
+            try:
+                dot = middleware_path.rindex('.')
+            except ValueError:
+                raise exceptions.ImproperlyConfigured, '%s isn\'t look like a middleware module' % middleware_path
             mw_module, mw_classname = middleware_path[:dot], middleware_path[dot+1:]
             try:
                 mod = __import__(mw_module, '', '', [''])