diff --git a/hgext/rebase.py b/hgext/rebase.py
index f19d5c852f9be42e9cfe5822c5d5f2fa6c076daf_aGdleHQvcmViYXNlLnB5..cd42f77d30c451bd74c2636f91afeb475cea4fdb_aGdleHQvcmViYXNlLnB5 100644
--- a/hgext/rebase.py
+++ b/hgext/rebase.py
@@ -210,7 +210,7 @@
                       " unrebased descendants"),
                     hint=_('use --keep to keep original changesets'))
             elif not keepf and not repo[root].mutable():
-                raise util.Abort(_("Can't rebase immutable changeset %s")
+                raise util.Abort(_("can't rebase immutable changeset %s")
                                  % repo[root],
                                  hint=_('see hg help phases for details'))
             else:
diff --git a/tests/test-rebase-scenario-global.t b/tests/test-rebase-scenario-global.t
index f19d5c852f9be42e9cfe5822c5d5f2fa6c076daf_dGVzdHMvdGVzdC1yZWJhc2Utc2NlbmFyaW8tZ2xvYmFsLnQ=..cd42f77d30c451bd74c2636f91afeb475cea4fdb_dGVzdHMvdGVzdC1yZWJhc2Utc2NlbmFyaW8tZ2xvYmFsLnQ= 100644
--- a/tests/test-rebase-scenario-global.t
+++ b/tests/test-rebase-scenario-global.t
@@ -277,7 +277,7 @@
 
   $ hg pull --config phases.publish=True -q -r 6 . # update phase of 6
   $ hg rebase -d 5 -b 6
-  abort: Can't rebase immutable changeset e1c4361dd923
+  abort: can't rebase immutable changeset e1c4361dd923
   (see hg help phases for details)
   [255]