diff --git a/lib/rexml/source.rb b/lib/rexml/source.rb
index ff887fc0..e1a466e9 100644
--- a/lib/rexml/source.rb
+++ b/lib/rexml/source.rb
@@ -77,6 +77,7 @@ def initialize(arg, encoding=nil)
         detect_encoding
       end
       @line = 0
+      @term_encord = {}
     end
 
     # The current buffer (what we're going to read next)
@@ -227,7 +228,7 @@ def read(term = nil, min_bytes = 1)
 
     def read_until(term)
       pattern = Private::PRE_DEFINED_TERM_PATTERNS[term] || /#{Regexp.escape(term)}/
-      term = encode(term)
+      term = @term_encord[term] ||= encode(term)
       until str = @scanner.scan_until(pattern)
         break if @source.nil?
         break if @source.eof?
diff --git a/test/test_document.rb b/test/test_document.rb
index cda4354f..609aeba2 100644
--- a/test/test_document.rb
+++ b/test/test_document.rb
@@ -403,6 +403,40 @@ def test_utf_16
           assert_equal(expected_xml, actual_xml)
         end
       end
+
+      class ReadUntilTest < Test::Unit::TestCase
+       def test_utf_8
+          xml = <<-EOX.force_encoding("ASCII-8BIT")
+<?xml version="1.0" encoding="UTF-8"?>
+<message testing=">">Hello world!</message>
+EOX
+          document = REXML::Document.new(xml)
+          assert_equal("UTF-8", document.encoding)
+          assert_equal(">", REXML::XPath.match(document, "/message")[0].attribute("testing").value)
+        end
+
+        def test_utf_16le
+          xml = <<-EOX.encode("UTF-16LE").force_encoding("ASCII-8BIT")
+<?xml version="1.0" encoding="UTF-16"?>
+<message testing=">">Hello world!</message>
+EOX
+          bom = "\ufeff".encode("UTF-16LE").force_encoding("ASCII-8BIT")
+          document = REXML::Document.new(bom + xml)
+          assert_equal("UTF-16", document.encoding)
+          assert_equal(">", REXML::XPath.match(document, "/message")[0].attribute("testing").value)
+        end
+
+        def test_utf_16be
+          xml = <<-EOX.encode("UTF-16BE").force_encoding("ASCII-8BIT")
+<?xml version="1.0" encoding="UTF-16"?>
+<message testing=">">Hello world!</message>
+EOX
+          bom = "\ufeff".encode("UTF-16BE").force_encoding("ASCII-8BIT")
+          document = REXML::Document.new(bom + xml)
+          assert_equal("UTF-16", document.encoding)
+          assert_equal(">", REXML::XPath.match(document, "/message")[0].attribute("testing").value)
+        end
+      end
     end
   end
 end