diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -167,10 +167,10 @@
 def _divertopener(opener, target):
     """build an opener that writes in 'target.a' instead of 'target'"""
 
-    def _divert(name, mode=b'r', checkambig=False):
+    def _divert(name, mode=b'r', checkambig=False, **kwargs):
         if name != target:
-            return opener(name, mode)
-        return opener(name + b".a", mode)
+            return opener(name, mode, **kwargs)
+        return opener(name + b".a", mode, **kwargs)
 
     return _divert
 
@@ -178,9 +178,10 @@
 def _delayopener(opener, target, buf):
     """build an opener that stores chunks in 'buf' instead of 'target'"""
 
-    def _delay(name, mode=b'r', checkambig=False):
+    def _delay(name, mode=b'r', checkambig=False, **kwargs):
         if name != target:
-            return opener(name, mode)
+            return opener(name, mode, **kwargs)
+        assert not kwargs
         return appender(opener, name, mode, buf)
 
     return _delay