--- a/contrib/packaging/hg-docker	Fri Jan 11 13:14:25 2019 +0100
+++ b/contrib/packaging/hg-docker	Fri Jan 11 14:55:31 2019 +0100
@@ -47,7 +47,7 @@
         df = fh.read()
 
     for k, v in args:
-        df = df.replace(b'%%%s%%' % k, v)
+        df = df.replace(bytes('%%%s%%' % k.decode(), 'utf-8'), v)
 
     return df