diff --git a/.gitignore b/.gitignore
index c33abaf..9f998c4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,6 @@ pkg
 doc
 mongo-ruby-driver-*.gem
 nbproject
+*.bundle
+*.o
+ext/cbson/Makefile
diff --git a/Rakefile b/Rakefile
index f236966..4b3befe 100644
--- a/Rakefile
+++ b/Rakefile
@@ -4,7 +4,10 @@ require 'fileutils'
 require 'rake'
 require 'rake/testtask'
 require 'rake/gempackagetask'
-require 'rake/contrib/rubyforgepublisher'
+begin
+  require 'rake/contrib/rubyforgepublisher'
+rescue LoadError
+end
 
 # NOTE: some of the tests assume Mongo is running
 Rake::TestTask.new do |t|
@@ -23,6 +26,14 @@ task :publish => [:rdoc] do
   Rake::RubyForgePublisher.new(GEM, RUBYFORGE_USER).upload
 end
 
+desc "Compile the extension"
+task :compile do
+  cd 'ext/cbson'
+  ruby 'extconf.rb'
+  sh 'make'
+  cp 'cbson.bundle', '../../lib/mongo/ext/cbson.bundle'
+end
+
 namespace :gem do
 
   desc "Install the gem locally"
diff --git a/ext/cbson/cbson.c b/ext/cbson/cbson.c
new file mode 100644
index 0000000..071fb9b
--- /dev/null
+++ b/ext/cbson/cbson.c
@@ -0,0 +1,76 @@
+#include "ruby.h"
+#include <assert.h>
+
+#define INITIAL_BUFFER_SIZE 256
+
+typedef struct {
+    char* buffer;
+    int size;
+    int position;
+} bson_buffer;
+
+static bson_buffer* buffer_new(void) {
+    bson_buffer* buffer;
+    buffer = (bson_buffer*)malloc(sizeof(bson_buffer));
+    assert(buffer);
+
+    buffer->size = INITIAL_BUFFER_SIZE;
+    buffer->position = 0;
+    buffer->buffer = (char*)malloc(INITIAL_BUFFER_SIZE);
+    assert(buffer->buffer);
+
+    return buffer;
+}
+
+static void buffer_free(bson_buffer* buffer) {
+    assert(buffer);
+    assert(buffer->buffer);
+
+    free(buffer->buffer);
+    free(buffer);
+}
+
+static void buffer_resize(bson_buffer* buffer, int min_length) {
+    int size = buffer->size;
+    if (size >= min_length) {
+        return;
+    }
+    while (size < min_length) {
+        size *= 2;
+    }
+    buffer->buffer = (char*)realloc(buffer->buffer, size);
+    assert(buffer->buffer);
+    buffer->size = size;
+}
+
+static void buffer_assure_space(bson_buffer* buffer, int size) {
+    if (buffer->position + size <= buffer->size) {
+        return;
+    }
+    buffer_resize(buffer, buffer->position + size);
+}
+
+/* returns offset for writing */
+static int buffer_save_bytes(bson_buffer* buffer, int size) {
+    buffer_assure_space(buffer, size);
+    int position = buffer->position;
+    buffer->position += size;
+    return position;
+}
+
+static void buffer_write_bytes(bson_buffer* buffer, const char* bytes, int size) {
+    buffer_assure_space(buffer, size);
+
+    memcpy(buffer->buffer + buffer->position, bytes, size);
+    buffer->position += size;
+}
+
+static VALUE method_serialize(VALUE self, VALUE doc) {
+    char data[5] = {0x05, 0x00, 0x00, 0x00, 0x00};
+    return rb_str_new(data, 5);
+}
+
+void Init_cbson() {
+    VALUE CBson = rb_define_module("CBson");
+    rb_define_module_function(CBson, "serialize", method_serialize, 1);
+}
diff --git a/ext/cbson/extconf.rb b/ext/cbson/extconf.rb
new file mode 100644
index 0000000..29f8fac
--- /dev/null
+++ b/ext/cbson/extconf.rb
@@ -0,0 +1,7 @@
+require 'mkmf'
+
+extension_name = 'cbson'
+
+dir_config(extension_name)
+
+create_makefile(extension_name)
diff --git a/lib/mongo/util/bson.rb b/lib/mongo/util/bson.rb
index c0e8af9..0ea4c79 100644
--- a/lib/mongo/util/bson.rb
+++ b/lib/mongo/util/bson.rb
@@ -72,21 +72,28 @@ class BSON
     @buf.to_a
   end
 
-  def serialize(obj)
-    raise "Document is null" unless obj
+  begin
+    require 'mongo/ext/cbson'
+    def serialize(obj)
+      @buf = ByteBuffer.new(CBson.serialize(obj))
+    end
+  rescue LoadError
+    def serialize(obj)
+      raise "Document is null" unless obj
 
-    @buf.rewind
-    # put in a placeholder for the total size
-    @buf.put_int(0)
+      @buf.rewind
+      # put in a placeholder for the total size
+      @buf.put_int(0)
 
-    # Write key/value pairs. Always write _id first if it exists.
-    oid = obj['_id'] || obj[:_id]
-    serialize_key_value('_id', oid) if oid
-    obj.each {|k, v| serialize_key_value(k, v) unless k == '_id' || k == :_id }
+      # Write key/value pairs. Always write _id first if it exists.
+      oid = obj['_id'] || obj[:_id]
+      serialize_key_value('_id', oid) if oid
+      obj.each {|k, v| serialize_key_value(k, v) unless k == '_id' || k == :_id }
 
-    serialize_eoo_element(@buf)
-    @buf.put_int(@buf.size, 0)
-    self
+      serialize_eoo_element(@buf)
+      @buf.put_int(@buf.size, 0)
+      self
+    end
   end
 
   def serialize_key_value(k, v)