diff --git a/Library/Homebrew/cask/quarantine.rb b/Library/Homebrew/cask/quarantine.rb
index e038011e64..446f42e3f3 100644
--- a/Library/Homebrew/cask/quarantine.rb
+++ b/Library/Homebrew/cask/quarantine.rb
@@ -33,7 +33,7 @@ module Cask
     def self.check_quarantine_support
       odebug "Checking quarantine support"
 
-      if !system_command(xattr, args: ["-h"], print_stderr: false).success?
+      if xattr.nil? || !system_command(xattr, args: ["-h"], print_stderr: false).success?
         odebug "There's no working version of `xattr` on this system."
         :xattr_broken
       elsif swift.nil?