diff --git a/tests/test_docs.py b/tests/test_docs.py
index a02f6510..07363535 100644
--- a/tests/test_docs.py
+++ b/tests/test_docs.py
@@ -36,4 +36,4 @@ def test_rst_file_syntax(filename):
         stdout=subprocess.PIPE
     )
     err = p.communicate()[1]
-    assert p.returncode == 0, err
+    assert p.returncode == 0, err.decode('utf8')