diff --git a/Library/Homebrew/test/diagnostic_spec.rb b/Library/Homebrew/test/diagnostic_spec.rb
index 6e2c092683..12a8e0c425 100644
--- a/Library/Homebrew/test/diagnostic_spec.rb
+++ b/Library/Homebrew/test/diagnostic_spec.rb
@@ -43,8 +43,10 @@ describe Homebrew::Diagnostic::Checks do
 
   specify "#check_access_lock_dir" do
     begin
+      prev_mode = HOMEBREW_LOCK_DIR.stat.mode
       mode = HOMEBREW_LOCK_DIR.stat.mode & 0777
       HOMEBREW_LOCK_DIR.chmod 0555
+      expect(HOMEBREW_LOCK_DIR.stat.mode).not_to eq(prev_mode)
 
       expect(subject.check_access_lock_dir)
         .to match("#{HOMEBREW_LOCK_DIR} isn't writable.")