1 files changed, 12 insertions, 2 deletions
diff --git a/spec/ruby/library/stringio/set_encoding_spec.rb b/spec/ruby/library/stringio/set_encoding_spec.rb
index 17aa7df23e..21d45750f3 100644
--- a/spec/ruby/library/stringio/set_encoding_spec.rb
+++ b/spec/ruby/library/stringio/set_encoding_spec.rb
@@ -2,9 +2,19 @@ require 'stringio'
 require_relative '../../spec_helper'
 
 describe "StringIO#set_encoding" do
-  it "sets the encoding of the underlying String" do
-    io = StringIO.new
+  it "sets the encoding of the underlying String if the String is not frozen" do
+    str = "".encode(Encoding::US_ASCII)
+
+    io = StringIO.new(str)
     io.set_encoding Encoding::UTF_8
     io.string.encoding.should == Encoding::UTF_8
   end
+
+  it "does not set the encoding of the underlying String if the String is frozen" do
+    str = "".encode(Encoding::US_ASCII).freeze
+
+    io = StringIO.new(str)
+    io.set_encoding Encoding::UTF_8
+    io.string.encoding.should == Encoding::US_ASCII
+  end
 end