Index: test/ruby/test_string.rb
===================================================================
--- test/ruby/test_string.rb	(revision 30814)
+++ test/ruby/test_string.rb	(working copy)
@@ -719,6 +719,15 @@ class TestString < Test::Unit::TestCase
     assert_nil(a.sub!(S('X'), S('Y')))
   end
 
+  def test_gsub_bang_encoding
+    a = S("a")
+    a.force_encoding Encoding::BINARY
+
+    a.gsub!(//) do '' end
+
+    assert_equal Encoding::BINARY, a.encoding
+  end
+
   def test_sub_hash
     assert_equal('azc', 'abc'.sub(/b/, "b" => "z"))
     assert_equal('ac', 'abc'.sub(/b/, {}))