diff --git a/Library/Homebrew/system_config.rb b/Library/Homebrew/system_config.rb
index 50853070fa..3e6740b005 100644
--- a/Library/Homebrew/system_config.rb
+++ b/Library/Homebrew/system_config.rb
@@ -139,6 +139,7 @@ class SystemConfig
         HOMEBREW_BREW_FILE
         HOMEBREW_COMMAND_DEPTH
         HOMEBREW_CURL
+        HOMEBREW_DISPLAY
         HOMEBREW_GIT
         HOMEBREW_GIT_CONFIG_FILE
         HOMEBREW_LIBRARY