diff --git a/lib/debug.rb b/lib/debug.rb
index 394a53e172..34d7d27406 100644
--- a/lib/debug.rb
+++ b/lib/debug.rb
@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 # Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
 # Copyright (C) 2000  Information-technology Promotion Agency, Japan
 # Copyright (C) 2000-2003  NAKAMURA, Hiroshi  <nahi@ruby-lang.org>