diff --git a/mercurial/manifest.py b/mercurial/manifest.py
--- a/mercurial/manifest.py
+++ b/mercurial/manifest.py
@@ -36,6 +36,8 @@ class manifest(revlog.revlog):
 
     def readdelta(self, node):
         r = self.rev(node)
+        if self._parentdelta:
+            return self.parse(mdiff.patchtext(self.revdiff(self.deltaparent(r), r)))
         return self.parse(mdiff.patchtext(self.revdiff(r - 1, r)))
 
     def read(self, node):