diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2653,22 +2653,13 @@ def debugrevlog(ui, repo, file_=None, **
                  " rawsize totalsize compression heads chainlen\n")
         ts = 0
         heads = set()
-        rindex = r.index
-
-        def chainbaseandlen(rev):
-            clen = 0
-            base = rindex[rev][3]
-            while base != rev:
-                clen += 1
-                rev = base
-                base = rindex[rev][3]
-            return base, clen
 
         for rev in xrange(numrevs):
             dbase = r.deltaparent(rev)
             if dbase == -1:
                 dbase = rev
-            cbase, clen = chainbaseandlen(rev)
+            cbase = r.chainbase(rev)
+            clen = r.chainlen(rev)
             p1, p2 = r.parentrevs(rev)
             rs = r.rawsize(rev)
             ts = ts + rs
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -350,6 +350,20 @@ class revlog(object):
             rev = base
             base = index[rev][3]
         return base
+    def chainlen(self, rev):
+        index = self.index
+        generaldelta = self._generaldelta
+        iterrev = rev
+        e = index[iterrev]
+        clen = 0
+        while iterrev != e[3]:
+            clen += 1
+            if generaldelta:
+                iterrev = e[3]
+            else:
+                iterrev -= 1
+            e = index[iterrev]
+        return clen
     def flags(self, rev):
         return self.index[rev][0] & 0xFFFF
     def rawsize(self, rev):