diff --git a/tool/merger.rb b/tool/merger.rb
index 0ad9dd3664..de122c47fd 100755
--- a/tool/merger.rb
+++ b/tool/merger.rb
@@ -180,6 +180,7 @@ else
     when /\A\d+:\d+\z/
       r = ['-r', rev]
     when /\A(\d+)-(\d+)\z/
+      rev = "#{$1.to_i-1}:#$2"
       r = ['-r', rev]
     when /\A\d+\z/
       r = ['-c', rev]