diff --git a/Library/Homebrew/diagnostic.rb b/Library/Homebrew/diagnostic.rb
index 0c2e7b2935..01aa5d7465 100644
--- a/Library/Homebrew/diagnostic.rb
+++ b/Library/Homebrew/diagnostic.rb
@@ -1068,7 +1068,7 @@ module Homebrew
 
         locale_variables = ENV.keys.grep(/^(?:LC_\S+|LANG|LANGUAGE)\Z/).sort
 
-        cask_environment_variables = (locale_variables + environment_variables).sort.each do |var|
+        cask_environment_variables = (locale_variables + environment_variables).sort.filter_map do |var|
           next unless ENV.key?(var)
 
           var = %Q(#{var}="#{ENV.fetch(var)}")