diff --git a/zuul/driver/github/githubconnection.py b/zuul/driver/github/githubconnection.py
index 4910e51..d3779d6 100644
--- a/zuul/driver/github/githubconnection.py
+++ b/zuul/driver/github/githubconnection.py
@@ -253,7 +253,7 @@
             raise webob.exc.HTTPUnauthorized(
                 'Please specify a X-Hub-Signature header with secret.')
 
-        payload_signature = 'sha1=' + hmac.new(secret,
+        payload_signature = 'sha1=' + hmac.new(secret.encode('utf-8'),
                                                body,
                                                hashlib.sha1).hexdigest()