diff --git a/lib/stringio.rb b/lib/stringio.rb
index 90741cbad..f7f0de801 100644
--- a/lib/stringio.rb
+++ b/lib/stringio.rb
@@ -678,6 +678,11 @@ def internal_encoding
     nil
   end
 
+  def set_encoding(enc)
+    @string = @string.encode(enc)
+    self
+  end
+
   protected
 
     # meant to be overwritten by developers