diff --git a/hgext/remotefilelog/basepack.py b/hgext/remotefilelog/basepack.py
--- a/hgext/remotefilelog/basepack.py
+++ b/hgext/remotefilelog/basepack.py
@@ -270,9 +270,9 @@ class versionmixin(object):
                 # only affect this instance
                 self.VERSION = version
             elif self.VERSION != version:
-                raise RuntimeError('inconsistent version: %s' % version)
+                raise RuntimeError('inconsistent version: %d' % version)
         else:
-            raise RuntimeError('unsupported version: %s' % version)
+            raise RuntimeError('unsupported version: %d' % version)
 
 class basepack(versionmixin):
     # The maximum amount we should read via mmap before remmaping so the old