diff --git a/hgext/convert/monotone.py b/hgext/convert/monotone.py
--- a/hgext/convert/monotone.py
+++ b/hgext/convert/monotone.py
@@ -138,7 +138,7 @@
                 raise error.Abort(_('bad mtn packet - no end of packet size'))
             lengthstr += read
         try:
-            length = long(lengthstr[:-1])
+            length = pycompat.long(lengthstr[:-1])
         except TypeError:
             raise error.Abort(_('bad mtn packet - bad packet size %s')
                 % lengthstr)