diff --git a/heat/engine/resources/aws/autoscaling/autoscaling_group.py b/heat/engine/resources/aws/autoscaling/autoscaling_group.py
index 4a41e5d949..e7613ecf41 100644
--- a/heat/engine/resources/aws/autoscaling/autoscaling_group.py
+++ b/heat/engine/resources/aws/autoscaling/autoscaling_group.py
@@ -397,16 +397,6 @@ class AutoScalingGroup(cooldown.CooldownMixin, instgrp.InstanceGroup):
 
         super(AutoScalingGroup, self).validate()
 
-    def _resolve_attribute(self, name):
-        """Resolves the resource's attributes.
-
-        heat extension: "InstanceList" returns comma delimited list of server
-        ip addresses.
-        """
-        if name == self.INSTANCE_LIST:
-            return u','.join(inst.FnGetAtt('PublicIp')
-                             for inst in grouputils.get_members(self)) or None
-
     def child_template(self):
         if self.properties[self.DESIRED_CAPACITY]:
             num_instances = self.properties[self.DESIRED_CAPACITY]
diff --git a/heat/engine/resources/openstack/heat/instance_group.py b/heat/engine/resources/openstack/heat/instance_group.py
index 48a0a0f427..92b10885ab 100644
--- a/heat/engine/resources/openstack/heat/instance_group.py
+++ b/heat/engine/resources/openstack/heat/instance_group.py
@@ -397,7 +397,7 @@ class InstanceGroup(stack_resource.StackResource):
         ip addresses.
         """
         if name == self.INSTANCE_LIST:
-            return u','.join(inst.FnGetAtt('PublicIp')
+            return u','.join(inst.FnGetAtt('PublicIp') or '0.0.0.0'
                              for inst in grouputils.get_members(self)) or None
 
     def _nested_output_defns(self, resource_names, get_attr_fn):