diff --git a/wcs/middleware.py b/wcs/middleware.py
index 61dc67564..47410e434 100644
--- a/wcs/middleware.py
+++ b/wcs/middleware.py
@@ -63,7 +63,7 @@ class PublisherInitialisationMiddleware(object):
                     query_string_allowed_vars.split(',')]
             had_session_variables = False
             session_variables = {}
-            for k, v in compat_request.form.items():
+            for k, v in list(compat_request.form.items()):
                 if k.startswith('session_var_'):
                     had_session_variables = True
                     session_variable = str(k[len('session_var_'):])