1 files changed, 7 insertions, 0 deletions
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 27077b425b..eeda96c9ef 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -3855,4 +3855,11 @@ __END__
       th.join
     end;
   end
+
+  def test_external_encoding_index
+    IO.pipe {|r, w|
+      assert_raise(TypeError) {Marshal.dump(r)}
+      assert_raise(TypeError) {Marshal.dump(w)}
+    }
+  end
 end