diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index adf00a50a07..a633af50580 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -801,7 +801,8 @@ def test_wait_when_sigchild_ignored(self):
                                  stdout=subprocess.PIPE, stderr=subprocess.PIPE)
             stdout, stderr = p.communicate()
             self.assertEqual(0, p.returncode, "sigchild_ignore.py exited"
-                             " non-zero with this error:\n%s" % stderr)
+                             " non-zero with this error:\n%s" %
+                             stderr.decode('utf8'))
 
 
     #