diff --git a/activesupport/lib/active_support/core_ext/string/output_safety.rb b/activesupport/lib/active_support/core_ext/string/output_safety.rb
index 6251f34daf107c2b3437536cbb6e1e79af163196..43b9fd4bf772eb7bef39b3bb4edd258068778d39 100644
--- a/activesupport/lib/active_support/core_ext/string/output_safety.rb
+++ b/activesupport/lib/active_support/core_ext/string/output_safety.rb
@@ -171,7 +171,7 @@ def safe_concat(value)
       original_concat(value)
     end
 
-    def initialize(*)
+    def initialize(str = '')
       @html_safe = true
       super
     end