cannot run histedit, strange message

[Uwe Brauer]

Hi 

I have a typo in a commit message so I thought to run 

 hg histedit

However I obtain a message I never saw before 
 abort: cannot edit history that contains merges

The change set whose message I want to change does not contain a merge,
but of course in this branch there have been merges, but some changesets
ago.

I can run uncommit, but I am wondering about the message honestly.

Regards

Uwe Brauer