diff --git a/lib/mongo.rb b/lib/mongo.rb
index c51e3ad..082fb42 100644
--- a/lib/mongo.rb
+++ b/lib/mongo.rb
@@ -1,8 +1,10 @@
-require 'mongo/mongo'
 require 'mongo/objectid'
 require 'mongo/dbref'
 require 'mongo/binary'
+require 'mongo/regexp_of_holding'
 require 'mongo/undefined'
+
+require 'mongo/mongo'
 require 'mongo/message'
 require 'mongo/db'
 require 'mongo/cursor'
diff --git a/lib/mongo/regexp_of_holding.rb b/lib/mongo/regexp_of_holding.rb
new file mode 100644
index 0000000..94de008
--- /dev/null
+++ b/lib/mongo/regexp_of_holding.rb
@@ -0,0 +1,40 @@
+# --
+# Copyright (C) 2008-2009 10gen Inc.
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Affero General Public License, version 3, as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License
+# for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+# ++
+
+module XGen
+  module Mongo
+    module Driver
+
+      # A Regexp that can hold on to extra options and ignore them. Mongo
+      # regexes may contain option characters beyond 'i', 'm', and 'x'. (Note
+      # that Mongo only uses those three, but that regexes coming from other
+      # languages may store different option characters.)
+      class RegexpOfHolding < Regexp
+
+        attr_accessor :extra_options_str
+
+        # +str+ and +options+ are the same as Regexp. +extra_options_str+
+        # contains all the other flags that were in Mongo but we do not use or
+        # understand.
+        def initialize(str, options, extra_options_str)
+          super(str, options)
+          @extra_options_str = extra_options_str
+        end
+      end
+
+    end
+  end
+end
diff --git a/lib/mongo/util/bson.rb b/lib/mongo/util/bson.rb
index 615a37b..8439e47 100644
--- a/lib/mongo/util/bson.rb
+++ b/lib/mongo/util/bson.rb
@@ -221,7 +221,8 @@ class BSON
     options |= Regexp::IGNORECASE if options_str.include?('i')
     options |= Regexp::MULTILINE if options_str.include?('m')
     options |= Regexp::EXTENDED if options_str.include?('x')
-    Regexp.new(str, options)
+    options_str.gsub!(/[imx]/, '') # Now remove the three we understand
+    XGen::Mongo::Driver::RegexpOfHolding.new(str, options, options_str)
   end
 
   def deserialize_string_data(buf)
@@ -342,7 +343,9 @@ class BSON
     options_str << 'i' if ((options & Regexp::IGNORECASE) != 0)
     options_str << 'm' if ((options & Regexp::MULTILINE) != 0)
     options_str << 'x' if ((options & Regexp::EXTENDED) != 0)
-    self.class.serialize_cstr(buf, options_str)
+    options_str << val.extra_options_str if val.respond_to?(:extra_options_str)
+    # Must store option chars in alphabetical order
+    self.class.serialize_cstr(buf, options_str.split(//).sort.uniq.join)
   end
 
   def serialize_oid_element(buf, key, val)
diff --git a/tests/test_bson.rb b/tests/test_bson.rb
index b561157..c05852a 100644
--- a/tests/test_bson.rb
+++ b/tests/test_bson.rb
@@ -59,7 +59,26 @@ class BSONTest < Test::Unit::TestCase
   def test_regex
     doc = {'doc' => /foobar/i}
     @b.serialize(doc)
-    assert_equal doc, @b.deserialize
+    doc2 = @b.deserialize
+    assert_equal doc, doc2
+
+    r = doc2['doc']
+    assert_kind_of XGen::Mongo::Driver::RegexpOfHolding, r
+    assert_equal '', r.extra_options_str
+
+    r.extra_options_str << 'zywcab'
+    assert_equal 'zywcab', r.extra_options_str
+
+    b = BSON.new
+    doc = {'doc' => r}
+    b.serialize(doc)
+    doc2 = nil
+    doc2 = b.deserialize
+    assert_equal doc, doc2
+
+    r = doc2['doc']
+    assert_kind_of XGen::Mongo::Driver::RegexpOfHolding, r
+    assert_equal 'abcwyz', r.extra_options_str # must be sorted
   end
 
   def test_boolean