diff --git a/ext/cgi/escape/escape.c b/ext/cgi/escape/escape.c
index 939b054..e8f64f6 100644
--- a/ext/cgi/escape/escape.c
+++ b/ext/cgi/escape/escape.c
@@ -30,7 +30,7 @@ preserve_original_state(VALUE orig, VALUE dest)
 {
     rb_enc_associate(dest, rb_enc_get(orig));
 
-    FL_SET_RAW(dest, FL_TEST_RAW(orig, FL_FREEZE|FL_TAINT));
+    RB_OBJ_INFECT_RAW(dest, orig);
 }
 
 static VALUE
@@ -69,7 +69,7 @@ optimized_escape_html(VALUE str)
 	return dest;
     }
     else {
-	return str;
+	return rb_str_dup(str);
     }
 }
 
diff --git a/test/cgi/test_cgi_util.rb b/test/cgi/test_cgi_util.rb
index 08c2ed2..e97de410 100644
--- a/test/cgi/test_cgi_util.rb
+++ b/test/cgi/test_cgi_util.rb
@@ -66,16 +66,23 @@ def test_cgi_escape_html_preserve_encoding
     assert_equal(Encoding::US_ASCII, CGI::escapeHTML("'&\"><".force_encoding("US-ASCII")).encoding)
     assert_equal(Encoding::ASCII_8BIT, CGI::escapeHTML("'&\"><".force_encoding("ASCII-8BIT")).encoding)
     assert_equal(Encoding::UTF_8, CGI::escapeHTML("'&\"><".force_encoding("UTF-8")).encoding)
+    assert_equal(Encoding::US_ASCII, CGI::escapeHTML("Ruby".force_encoding("US-ASCII")).encoding)
+    assert_equal(Encoding::ASCII_8BIT, CGI::escapeHTML("Ruby".force_encoding("ASCII-8BIT")).encoding)
+    assert_equal(Encoding::UTF_8, CGI::escapeHTML("Ruby".force_encoding("UTF-8")).encoding)
   end
 
   def test_cgi_escape_html_preserve_tainted
     assert_equal(false, CGI::escapeHTML("'&\"><").tainted?)
     assert_equal(true, CGI::escapeHTML("'&\"><".taint).tainted?)
+    assert_equal(false, CGI::escapeHTML("Ruby").tainted?)
+    assert_equal(true, CGI::escapeHTML("Ruby".taint).tainted?)
   end
 
-  def test_cgi_escape_html_preserve_frozen
+  def test_cgi_escape_html_dont_freeze
     assert_equal(false, CGI::escapeHTML("'&\"><".dup).frozen?)
-    assert_equal(true, CGI::escapeHTML("'&\"><".freeze).frozen?)
+    assert_equal(false, CGI::escapeHTML("'&\"><".freeze).frozen?)
+    assert_equal(false, CGI::escapeHTML("Ruby".dup).frozen?)
+    assert_equal(false, CGI::escapeHTML("Ruby".freeze).frozen?)
   end
 
   def test_cgi_unescapeHTML