diff --git a/heat/engine/resources/openstack/heat/autoscaling_group.py b/heat/engine/resources/openstack/heat/autoscaling_group.py
index 1eb4976305..5b31a240e9 100644
--- a/heat/engine/resources/openstack/heat/autoscaling_group.py
+++ b/heat/engine/resources/openstack/heat/autoscaling_group.py
@@ -226,7 +226,7 @@ class AutoScalingResourceGroup(aws_asg.AutoScalingGroup):
                 output_name = attr
             else:
                 key, path = attr[0], list(attr[1:])
-                output_name = ', '.join(attr)
+                output_name = ', '.join(six.text_type(a) for a in attr)
 
             if key.startswith("resource."):
                 keycomponents = key.split('.', 2)
diff --git a/heat/engine/resources/openstack/heat/resource_chain.py b/heat/engine/resources/openstack/heat/resource_chain.py
index 0d3973348c..42362584e3 100644
--- a/heat/engine/resources/openstack/heat/resource_chain.py
+++ b/heat/engine/resources/openstack/heat/resource_chain.py
@@ -166,7 +166,7 @@ class ResourceChain(stack_resource.StackResource):
                 output_name = attr
             else:
                 key, path = attr[0], list(attr[1:])
-                output_name = ', '.join(attr)
+                output_name = ', '.join(six.text_type(a) for a in attr)
 
             if key.startswith("resource."):
                 keycomponents = key.split('.', 2)
diff --git a/heat/engine/resources/openstack/heat/resource_group.py b/heat/engine/resources/openstack/heat/resource_group.py
index 3351395277..10fba283c2 100644
--- a/heat/engine/resources/openstack/heat/resource_group.py
+++ b/heat/engine/resources/openstack/heat/resource_group.py
@@ -462,7 +462,7 @@ class ResourceGroup(stack_resource.StackResource):
                 output_name = attr
             else:
                 key, path = attr[0], list(attr[1:])
-                output_name = ', '.join(attr)
+                output_name = ', '.join(six.text_type(a) for a in attr)
 
             if key.startswith("resource."):
                 keycomponents = key.split('.', 2)
diff --git a/heat/tests/autoscaling/test_heat_scaling_group.py b/heat/tests/autoscaling/test_heat_scaling_group.py
index 5f913adae1..3446331539 100644
--- a/heat/tests/autoscaling/test_heat_scaling_group.py
+++ b/heat/tests/autoscaling/test_heat_scaling_group.py
@@ -42,6 +42,13 @@ class TestAutoScalingGroupValidation(common.HeatTestCase):
         self.assertRaises(exception.StackValidationFailed,
                           stack['my-group'].validate)
 
+    def test_validate_reference_attr_with_none_ref(self):
+        stack = utils.parse_stack(self.parsed)
+        group = stack['my-group']
+        self.patchobject(group, 'referenced_attrs',
+                         return_value=set([('something', None)]))
+        self.assertIsNone(group.validate())
+
 
 class TestScalingGroupTags(common.HeatTestCase):
     def setUp(self):
diff --git a/heat/tests/openstack/heat/test_resource_chain.py b/heat/tests/openstack/heat/test_resource_chain.py
index f352ec5614..10ab7f0e6e 100644
--- a/heat/tests/openstack/heat/test_resource_chain.py
+++ b/heat/tests/openstack/heat/test_resource_chain.py
@@ -129,6 +129,12 @@ class ResourceChainTest(common.HeatTestCase):
         chain = self._create_chain(TEMPLATE)
         chain.validate_nested_stack()
 
+    def test_validate_reference_attr_with_none_ref(self):
+        chain = self._create_chain(TEMPLATE)
+        self.patchobject(chain, 'referenced_attrs',
+                         return_value=set([('config', None)]))
+        self.assertIsNone(chain.validate())
+
     def test_validate_incompatible_properties(self):
         # Tests a resource in the chain that does not support the properties
         # specified to each resource.
diff --git a/heat/tests/openstack/heat/test_resource_group.py b/heat/tests/openstack/heat/test_resource_group.py
index 75bff2dfd4..91174abf81 100644
--- a/heat/tests/openstack/heat/test_resource_group.py
+++ b/heat/tests/openstack/heat/test_resource_group.py
@@ -507,6 +507,14 @@ class ResourceGroupTest(common.HeatTestCase):
         resgrp = resource_group.ResourceGroup('test', snip, stack)
         self.assertIsNone(resgrp.validate())
 
+    def test_validate_reference_attr_with_none_ref(self):
+        stack = utils.parse_stack(template_attr)
+        snip = stack.t.resource_definitions(stack)['group1']
+        resgrp = resource_group.ResourceGroup('test', snip, stack)
+        self.patchobject(resgrp, 'referenced_attrs',
+                         return_value=set([('nested_dict', None)]))
+        self.assertIsNone(resgrp.validate())
+
     def test_invalid_removal_policies_nolist(self):
         """Test that error raised for malformed removal_policies."""
         tmp = copy.deepcopy(template)