diff --git a/Library/Homebrew/cmd/test-bot.rb b/Library/Homebrew/cmd/test-bot.rb
index caa1907846..317c78aae2 100644
--- a/Library/Homebrew/cmd/test-bot.rb
+++ b/Library/Homebrew/cmd/test-bot.rb
@@ -710,6 +710,7 @@ module Homebrew
     end
 
     ENV["HOMEBREW_DEVELOPER"] = "1"
+    ENV["HOMEBREW_SANDBOX"] = "1"
     ENV["HOMEBREW_NO_EMOJI"] = "1"
     if ARGV.include?("--ci-master") || ARGV.include?("--ci-pr") \
        || ARGV.include?("--ci-testing")