gistfile1.diff

diff --git a/lib/cgi/util.rb b/lib/cgi/util.rb
index 2bb3b0d..f08a23c 100644
--- a/lib/cgi/util.rb
+++ b/lib/cgi/util.rb
@@ -4,9 +4,15 @@ class CGI
   #   url_encoded_string = CGI::escape("'Stop!' said Fred")
   #      # => "%27Stop%21%27+said+Fred"
   def CGI::escape(string)
+    unless string.valid_encoding?
+      encoding = string.encoding
+      string = string.dup.force_encoding('ASCII-8BIT')
+    end
     string.gsub(/([^ a-zA-Z0-9_.-]+)/) do
       '%' + $1.unpack('H2' * $1.bytesize).join('%').upcase
-    end.tr(' ', '+')
+    end.tr(' ', '+').tap do |result|
+      result.force_encoding(encoding) if encoding
+    end
   end
 
   # URL-decode a string with encoding(optional).
diff --git a/test/cgi/test_cgi_util.rb b/test/cgi/test_cgi_util.rb
index 71e8bea..f34703e 100644
--- a/test/cgi/test_cgi_util.rb
+++ b/test/cgi/test_cgi_util.rb
@@ -24,6 +24,12 @@ class CGIUtilTest < Test::Unit::TestCase
     assert_equal('%26%3C%3E%22+%E3%82%86%E3%82%93%E3%82%86%E3%82%93'.ascii_only?, CGI::escape(@str1).ascii_only?) if defined?(::Encoding)
   end
 
+  def test_cgi_escape_with_invalid_byte_sequence
+    assert_nothing_raised(ArgumentError) do
+      assert_equal('%C0%3C%3C', CGI::escape("\xC0<<".force_encoding("UTF-8")))
+    end
+  end
+
   def test_cgi_unescape
     assert_equal(@str1, CGI::unescape('%26%3C%3E%22+%E3%82%86%E3%82%93%E3%82%86%E3%82%93'))
     assert_equal(@str1.encoding, CGI::unescape('%26%3C%3E%22+%E3%82%86%E3%82%93%E3%82%86%E3%82%93').encoding) if defined?(::Encoding)