diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -1760,6 +1760,7 @@
         self._updatebar(self.topic, self.pos, b"", self.unit, self.total)
 
     def _printdebug(self, item):
+        unit = b''
         if self.unit:
             unit = b' ' + self.unit
         if item: