diff --git a/heat/api/openstack/v1/stacks.py b/heat/api/openstack/v1/stacks.py
index 9cb39495f4..853334debf 100644
--- a/heat/api/openstack/v1/stacks.py
+++ b/heat/api/openstack/v1/stacks.py
@@ -71,9 +71,10 @@ class InstantiationData(object):
                 return environment_format.parse(data)
             else:
                 return template_format.parse(data)
-        except ValueError:
-            err_reason = _("%s not in valid format") % data_type
-            raise exc.HTTPBadRequest(err_reason)
+        except ValueError as parse_ex:
+            mdict = {'type': data_type, 'error': parse_ex}
+            msg = _("%(type)s not in valid format: %(error)s") % mdict
+            raise exc.HTTPBadRequest(msg)
 
     def stack_name(self):
         """
diff --git a/heat/tests/test_api_openstack_v1.py b/heat/tests/test_api_openstack_v1.py
index 8f4197038e..e0ad05d0fc 100644
--- a/heat/tests/test_api_openstack_v1.py
+++ b/heat/tests/test_api_openstack_v1.py
@@ -71,6 +71,20 @@ class InstantiationDataTest(HeatTestCase):
                           stacks.InstantiationData.format_parse,
                           '!@#$%^&not json', 'Garbage')
 
+    def test_format_parse_invalid_message(self):
+        # make sure the parser error gets through to the caller.
+        bad_temp = '''
+parameters:
+  KeyName:
+     type: string
+    description: bla
+        '''
+
+        parse_ex = self.assertRaises(webob.exc.HTTPBadRequest,
+                                     stacks.InstantiationData.format_parse,
+                                     bad_temp, 'foo')
+        self.assertIn('line 3, column 3', str(parse_ex))
+
     def test_stack_name(self):
         body = {'stack_name': 'wibble'}
         data = stacks.InstantiationData(body)