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 c761325108..042283e4fc 100644
--- a/activesupport/lib/active_support/core_ext/string/output_safety.rb
+++ b/activesupport/lib/active_support/core_ext/string/output_safety.rb
@@ -150,7 +150,7 @@ module ActiveSupport #:nodoc:
       else
         if html_safe?
           new_safe_buffer = super
-          new_safe_buffer.instance_eval { @html_safe = true }
+          new_safe_buffer.instance_variable_set :@html_safe, true
           new_safe_buffer
         else
           to_str[*args]