diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index 67346a0..6ba8022 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -13,6 +13,7 @@
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 require 'socket'
+require 'mongo/objectid'
 require 'mongo/collection'
 require 'mongo/message'
 require 'mongo/query'
@@ -152,6 +153,7 @@ module XGen
         end
 
         def insert_into_db(collection, objects)
+          objects.each { |o| o['_id'] ||= ObjectID.new }
           # TODO synchronize
           objects.each { |o| send_to_db(InsertMessage.new(@name, collection, o)) }
         end
@@ -177,4 +179,3 @@ module XGen
     end
   end
 end
-
diff --git a/lib/mongo/objectid.rb b/lib/mongo/objectid.rb
index bdbf310..cd96941 100644
--- a/lib/mongo/objectid.rb
+++ b/lib/mongo/objectid.rb
@@ -20,12 +20,18 @@ module XGen
 
       class ObjectID
 
+        UUID_STRING_LENGTH = 24
+
+        @@uuid_generator = UUID.new
+
         # String UUID
         attr_reader :uuid
 
-        # uuid is a string
+        # +uuid+ is a string. If nil, a new UUID will be generated.
         def initialize(uuid=nil)
-          @uuid ||= UUID.new.generate
+          # The Babble server expects 12-byte (24 hex character) keys, which
+          # is why we throw away part of the UUID.
+          @uuid ||= @@uuid_generator.generate(:compact).sub(/(.{12}).{8}(.{12})/, '\1\2')
         end
 
         def to_s
diff --git a/lib/mongo/util/bson.rb b/lib/mongo/util/bson.rb
index 5f945ce..49f4fbd 100644
--- a/lib/mongo/util/bson.rb
+++ b/lib/mongo/util/bson.rb
@@ -155,8 +155,8 @@ class BSON
     bytes[0..-2].pack("C*")
   end
 
-  def deserialize_oid_data
-    XGen::Mongo::Driver::ObjectID.new(buf.get(12).pack("C*"))
+  def deserialize_oid_data(buf)
+    XGen::Mongo::Driver::ObjectID.new(buf.get(XGen::Mongo::Driver::ObjectID::UUID_STRING_LENGTH).pack("C*"))
   end
 
   def serialize_eoo_element(buf)
@@ -199,7 +199,7 @@ class BSON
   def serialize_oid_element(buf, key, val)
     buf.put(OID)
     self.class.serialize_cstr(buf, key)
-    buf.put_array(val.to_a)
+    buf.put_array(val.to_s.unpack("C*"))
   end
 
   def serialize_string_element(buf, key, val, type)