diff --git a/contrib/python3-whitelist b/contrib/python3-whitelist
--- a/contrib/python3-whitelist
+++ b/contrib/python3-whitelist
@@ -121,6 +121,7 @@
 test-convert-hg-sink.t
 test-convert-hg-source.t
 test-convert-hg-startrev.t
+test-convert-mtn.t
 test-convert-splicemap.t
 test-convert-svn-sink.t
 test-convert-tagsbranch-topology.t
diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -70,7 +70,10 @@
 
 def encodeextra(d):
     # keys must be sorted to produce a deterministic changelog entry
-    items = [_string_escape('%s:%s' % (k, d[k])) for k in sorted(d)]
+    items = [
+        _string_escape('%s:%s' % (k, pycompat.bytestr(d[k])))
+        for k in sorted(d)
+    ]
     return "\0".join(items)
 
 def stripdesc(desc):