diff --git a/Library/Homebrew/formula_auditor.rb b/Library/Homebrew/formula_auditor.rb
index 4c574caf43..99aa219f5b 100644
--- a/Library/Homebrew/formula_auditor.rb
+++ b/Library/Homebrew/formula_auditor.rb
@@ -470,7 +470,7 @@ module Homebrew
       return unless @core_tap
       return unless formula.keg_only?
 
-      keg_only_message = text.to_s.match(/keg_only\s+["'](.*)["']/)&.captures.first
+      keg_only_message = text.to_s.match(/keg_only\s+["'](.*)["']/)&.captures&.first
       return unless keg_only_message&.include?("HOMEBREW_PREFIX")
 
       problem "`keg_only` reason should not include `HOMEBREW_PREFIX` as it creates confusing `brew info` output."