diff --git a/heatclient/tests/test_environment_format.py b/heatclient/tests/test_environment_format.py
index b972eeab..a615784f 100644
--- a/heatclient/tests/test_environment_format.py
+++ b/heatclient/tests/test_environment_format.py
@@ -52,14 +52,14 @@ parameters: }
     def test_parse_string_environment(self):
         env = 'just string'
         expect = 'The environment is not a valid YAML mapping data type.'
-        msg = self.assertRaises(ValueError, environment_format.parse, env)
-        self.assertIn(expect, msg)
+        e = self.assertRaises(ValueError, environment_format.parse, env)
+        self.assertIn(expect, str(e))
 
     def test_parse_document(self):
         env = '["foo" , "bar"]'
         expect = 'The environment is not a valid YAML mapping data type.'
-        msg = self.assertRaises(ValueError, environment_format.parse, env)
-        self.assertIn(expect, msg)
+        e = self.assertRaises(ValueError, environment_format.parse, env)
+        self.assertIn(expect, str(e))
 
 
 class YamlParseExceptions(testtools.TestCase):