diff --git a/tool/redmine-backporter.rb b/tool/redmine-backporter.rb
index 843132ab3a..73d375b146 100755
--- a/tool/redmine-backporter.rb
+++ b/tool/redmine-backporter.rb
@@ -358,7 +358,7 @@ eom
       str = log[/merge revision\(s\) ([^:]+)(?=:)/]
       if str
         str.sub!(/\Amerge/, 'merged')
-        str.gsub!(/\h{40}/, 'commit:\0')
+        str.gsub!(/\h{8,40}/, 'commit:\0')
         str = "ruby_#{TARGET_VERSION.tr('.','_')} commit:#{rev} #{str}."
       else
         str = "ruby_#{TARGET_VERSION.tr('.','_')} commit:#{rev}."