diff --git a/Library/Homebrew/extend/os/mac/diagnostic.rb b/Library/Homebrew/extend/os/mac/diagnostic.rb
index 00a297d34b..25b451e9f0 100644
--- a/Library/Homebrew/extend/os/mac/diagnostic.rb
+++ b/Library/Homebrew/extend/os/mac/diagnostic.rb
@@ -314,6 +314,7 @@ module Homebrew
       end
 
       def check_for_beta_xquartz
+        return unless MacOS::XQuartz.version
         return unless MacOS::XQuartz.version.include? "beta"
 
         <<-EOS.undent