diff --git a/hgext3rd/tweakdefaults.py b/hgext3rd/tweakdefaults.py
--- a/hgext3rd/tweakdefaults.py
+++ b/hgext3rd/tweakdefaults.py
@@ -674,7 +674,8 @@
     # oldnode was not updated if newnodes is an iterable
     if len(newnodes) == 1:
         newnode = newnodes[0]
-        firstline = repo[newnode].description().split("\n")[0][:50]
+        firstline = encoding.trim(
+            repo[newnode].description().split("\n")[0], 50, '...')
         repo.ui.status(_("%s -> %s \"%s\"\n") % (
             short(oldnode), short(newnode), firstline))
 
diff --git a/tests/test-tweakdefaults.t b/tests/test-tweakdefaults.t
--- a/tests/test-tweakdefaults.t
+++ b/tests/test-tweakdefaults.t
@@ -631,6 +631,14 @@
   ee71024c6e8c -> 0c42bb4bf23f "2"
   saved backup bundle to $TESTTMP/showupdated/.hg/strip-backup/6e3ddf6f49ef-4b18babd-rebase.hg (glob)
 
+Test rebase with showupdate=True and a long commit message
+  $ touch longfile && hg add -q
+  $ hg commit -qm "This is a long commit message which will be truncated."
+  $ hg rebase -d 1
+  rebasing 14:e915a57d67db "This is a long commit message which will be truncated." (tip)
+  e915a57d67db -> 5444f740ff6c "This is a long commit message which will be tru..."
+  saved backup bundle to $TESTTMP/showupdated/.hg/strip-backup/e915a57d67db-ad3372b5-rebase.hg (glob)
+
 Test bookmark -D
   $ cd $TESTTMP
   $ hg init book-D