diff --git a/heat/engine/api.py b/heat/engine/api.py
index f80b05ef49..049043f603 100644
--- a/heat/engine/api.py
+++ b/heat/engine/api.py
@@ -367,7 +367,7 @@ def format_stack_resource(resource, detail=True, with_props=False,
 def format_stack_preview(stack):
     def format_resource(res):
         if isinstance(res, list):
-            return map(format_resource, res)
+            return list(map(format_resource, res))
         return format_stack_resource(res, with_props=True)
 
     fmt_stack = format_stack(stack, preview=True)
diff --git a/heat_integrationtests/functional/test_preview.py b/heat_integrationtests/functional/test_preview.py
index 99c24ebd3b..4b9d77c6b5 100644
--- a/heat_integrationtests/functional/test_preview.py
+++ b/heat_integrationtests/functional/test_preview.py
@@ -222,8 +222,16 @@ resources:
             stack_name=stack_name,
             template=main_template,
             files={'nested.yaml': nested_template}).to_dict()
+
+        resource_names = []
+
+        def get_resource_names(resources):
+            for item in resources:
+                if isinstance(item, dict):
+                    resource_names.append(item['resource_name'])
+                else:
+                    get_resource_names(item)
+        get_resource_names(result['resources'])
         # ensure that fixed network and port here
-        self.assertEqual('fixed_network',
-                         result['resources'][0]['resource_name'])
-        self.assertEqual('port',
-                         result['resources'][1][0][0]['resource_name'])
+        self.assertIn('fixed_network', resource_names)
+        self.assertIn('port', resource_names)