diff --git a/git-filter-repo b/git-filter-repo
index 10401e4..8fc4745 100755
--- a/git-filter-repo
+++ b/git-filter-repo
@@ -1862,7 +1862,7 @@ EXAMPLES
                "part of git history, historical versions of the file will "
                "be ignored; only the current contents are consulted."))
     people.add_argument('--use-mailmap', dest='mailmap',
-        action='store_const', const='.mailmap',
+        action='store_const', const=b'.mailmap',
         help=_("Same as: '--mailmap .mailmap' "))
 
     parents = parser.add_argument_group(title=_("Parent rewriting"))