diff --git a/mercurial/upgrade.py b/mercurial/upgrade.py
--- a/mercurial/upgrade.py
+++ b/mercurial/upgrade.py
@@ -480,11 +480,13 @@
             mrevcount += len(rl)
             msrcsize += datasize
             mrawsize += rawsize
-        elif isinstance(rl, revlog.revlog):
+        elif isinstance(rl, filelog.filelog):
             fcount += 1
             frevcount += len(rl)
             fsrcsize += datasize
             frawsize += rawsize
+        else:
+            error.ProgrammingError('unknown revlog type')
 
     if not revcount:
         return