diff --git a/tempest/tests/test_wrappers.py b/tempest/tests/test_wrappers.py
index bba4012..f6830a1 100644
--- a/tempest/tests/test_wrappers.py
+++ b/tempest/tests/test_wrappers.py
@@ -69,7 +69,7 @@
 
         self.assertEqual(
             p.returncode, expected,
-            "Stdout: %s; Stderr: %s" % (p.stdout, p.stderr))
+            "Stdout: %s; Stderr: %s" % (p.stdout.read(), p.stderr.read()))
 
     def test_pretty_tox(self):
         # Git init is required for the pbr testr command. pbr requires a git