diff --git a/mercurial/rewriteutil.py b/mercurial/rewriteutil.py
--- a/mercurial/rewriteutil.py
+++ b/mercurial/rewriteutil.py
@@ -44,7 +44,7 @@
         revs = (r.rev() for r in revs)
 
     if len(repo[None].parents()) > 1:
-        raise error.StateError(_(b"cannot %s while merging") % action)
+        raise error.StateError(_(b"cannot %s changesets while merging") % action)
 
     publicrevs = repo.revs(b'%ld and public()', revs)
     if publicrevs:
diff --git a/tests/test-commit-amend.t b/tests/test-commit-amend.t
--- a/tests/test-commit-amend.t
+++ b/tests/test-commit-amend.t
@@ -406,7 +406,7 @@
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ hg ci --amend
-  abort: cannot amend while merging
+  abort: cannot amend changesets while merging
   [20]
   $ hg ci -m 'merge'
 
diff --git a/tests/test-uncommit.t b/tests/test-uncommit.t
--- a/tests/test-uncommit.t
+++ b/tests/test-uncommit.t
@@ -410,7 +410,7 @@
   [20]
 
   $ hg uncommit --config experimental.uncommitondirtywdir=True
-  abort: cannot uncommit while merging
+  abort: cannot uncommit changesets while merging
   [20]
 
   $ hg status