diff --git a/tool/redmine-backporter.rb b/tool/redmine-backporter.rb
index 826548f000..3466d646e0 100755
--- a/tool/redmine-backporter.rb
+++ b/tool/redmine-backporter.rb
@@ -77,7 +77,7 @@ class String
       seq << "\e[#{c}m"
     end
     if back
-      c = COLORS[back]
+      c = COLORS[back] + 10
       raise "unknown background color #{back}" unless c
       seq << "\e[#{c}m"
     end