diff --git a/tool/redmine-backporter.rb b/tool/redmine-backporter.rb
index 4c5476fa7d..1b25cd3e4f 100755
--- a/tool/redmine-backporter.rb
+++ b/tool/redmine-backporter.rb
@@ -422,7 +422,7 @@ eom
   },
 
   "done" => proc{|args|
-    raise CommandSyntaxError unless /\A(\d+)?(?: -- +(.*))?\z/ =~ args
+    raise CommandSyntaxError unless /\A(\d+)?(?:\s*-- +(.*))?\z/ =~ args
     notes = $2
     notes.strip! if notes
     if $1