diff --git a/django/template/defaulttags.py b/django/template/defaulttags.py
index 8b52b70cda..88cb5f68be 100644
--- a/django/template/defaulttags.py
+++ b/django/template/defaulttags.py
@@ -88,6 +88,8 @@ class ForNode(Node):
             values = []
         if values is None:
             values = []
+        if not hasattr(values, '__len__'):
+            values = list(values)
         len_values = len(values)
         if self.reversed:
             # From http://www.python.org/doc/current/tut/node11.html