diff --git a/mrbgems/mruby-string-ext/mrblib/string.rb b/mrbgems/mruby-string-ext/mrblib/string.rb
index aa788303e..3e56ab76e 100644
--- a/mrbgems/mruby-string-ext/mrblib/string.rb
+++ b/mrbgems/mruby-string-ext/mrblib/string.rb
@@ -98,8 +98,10 @@ class String
       lines.each do |line|
         blk.call(line)
       end
+      self
+    else
+      lines
     end
-    lines
   end
 
   ##