diff --git a/heat/engine/api.py b/heat/engine/api.py
index e03a46e039..ceb881470b 100644
--- a/heat/engine/api.py
+++ b/heat/engine/api.py
@@ -220,7 +220,7 @@ def format_stack(stack, preview=False, resolve_outputs=True):
         rpc_api.STACK_OWNER: stack.username,
         rpc_api.STACK_PARENT: stack.owner_id,
         rpc_api.STACK_USER_PROJECT_ID: stack.stack_user_project_id,
-        rpc_api.STACK_TAGS: stack.tags or None,
+        rpc_api.STACK_TAGS: stack.tags,
     }
 
     if not preview:
diff --git a/heat/tests/test_engine_api_utils.py b/heat/tests/test_engine_api_utils.py
index d7d4ea6eb8..8703fcdda3 100644
--- a/heat/tests/test_engine_api_utils.py
+++ b/heat/tests/test_engine_api_utils.py
@@ -397,7 +397,7 @@ class FormatTest(common.HeatTestCase):
             'outputs': [],
             'template_description': 'No description',
             'timeout_mins': None,
-            'tags': None,
+            'tags': [],
             'parameters': {
                 'AWS::Region': 'ap-southeast-1',
                 'AWS::StackId': aws_id,