Index: test/ruby/test_string.rb
===================================================================
--- test/ruby/test_string.rb	(revision 30814)
+++ test/ruby/test_string.rb	(working copy)
@@ -153,6 +153,18 @@ class TestString < Test::Unit::TestCase
     assert_raise(ArgumentError) { "foo"[1, 2, 3] = "" }
   end
 
+  def test_ASET_encoding
+    a = S("a")
+    a.force_encoding Encoding::US_ASCII
+
+    r = S("")
+    r.force_encoding Encoding::UTF_8
+
+    a[/a/] = r
+
+    assert_equal Encoding::US_ASCII, a.encoding
+  end
+
   def test_CMP # '<=>'
     assert_equal(1, S("abcdef") <=> S("abcde"))
     assert_equal(0, S("abcdef") <=> S("abcdef"))