diff --git a/hgext/amend.py b/hgext/amend.py
--- a/hgext/amend.py
+++ b/hgext/amend.py
@@ -16,7 +16,6 @@
 from mercurial import (
     cmdutil,
     commands,
-    pycompat,
     registrar,
 )
 
@@ -66,7 +65,7 @@
 
     See :hg:`help commit` for more details.
     """
-    cmdutil.checknotesize(ui, pycompat.byteskwargs(opts))
+    cmdutil.check_note_size(opts)
 
     with repo.wlock(), repo.lock():
         if not opts.get('logfile'):
diff --git a/hgext/uncommit.py b/hgext/uncommit.py
--- a/hgext/uncommit.py
+++ b/hgext/uncommit.py
@@ -153,9 +153,8 @@
     If no files are specified, the commit will be pruned, unless --keep is
     given.
     """
+    cmdutil.check_note_size(opts)
     opts = pycompat.byteskwargs(opts)
-
-    cmdutil.checknotesize(ui, opts)
     cmdutil.resolvecommitoptions(ui, opts)
 
     with repo.wlock(), repo.lock():
diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -328,10 +328,10 @@
     return datemaydiffer
 
 
-def checknotesize(ui, opts):
+def check_note_size(opts):
     """make sure note is of valid format"""
 
-    note = opts.get(b'note')
+    note = opts.get('note')
     if not note:
         return