diff --git a/Library/Homebrew/cmd/test-bot.rb b/Library/Homebrew/cmd/test-bot.rb
index 9859ea6e4c..b0c40bbea7 100644
--- a/Library/Homebrew/cmd/test-bot.rb
+++ b/Library/Homebrew/cmd/test-bot.rb
@@ -336,6 +336,7 @@ module Homebrew
       # Handle formulae arguments being passed on the command-line e.g. `brew test-bot wget fish`.
       elsif @formulae && @formulae.any?
         @name = "#{@formulae.first}-#{diff_end_sha1}"
+        diff_start_sha1 = diff_end_sha1
       # Handle a hash being passed on the command-line e.g. `brew test-bot 1a2b3c`.
       elsif @hash
         test "git", "checkout", @hash