diff --git a/Library/Homebrew/dev-cmd/test-bot.rb b/Library/Homebrew/dev-cmd/test-bot.rb
index d321ef8877..3579e9f79e 100644
--- a/Library/Homebrew/dev-cmd/test-bot.rb
+++ b/Library/Homebrew/dev-cmd/test-bot.rb
@@ -273,11 +273,11 @@ module Homebrew
       def diff_formulae(start_revision, end_revision, path, filter)
         return unless @tap
         git(
-          "diff-tree", "--name-only", "--diff-filter=#{filter}",
+          "diff-tree", "-r", "--name-only", "--diff-filter=#{filter}",
           start_revision, end_revision, "--", path
         ).lines.map do |line|
           file = Pathname.new line.chomp
-          next unless file.extname == ".rb"
+          next unless @tap.formula_file?(file)
           @tap.formula_file_to_name(file)
         end.compact
       end