diff --git a/ext/cbson/cbson.c b/ext/cbson/cbson.c
index 065f23c..4c0c9ce 100644
--- a/ext/cbson/cbson.c
+++ b/ext/cbson/cbson.c
@@ -904,8 +904,9 @@ static VALUE objectid_generate(VALUE self)
     return oid;
 }
 
-static void method_update_max_bson_size(VALUE self, VALUE connection) {
+static VALUE method_update_max_bson_size(VALUE self, VALUE connection) {
     max_bson_size = FIX2INT(rb_funcall(connection, rb_intern("max_bson_size"), 0));
+    return INT2FIX(max_bson_size);
 }
 
 static VALUE method_max_bson_size(VALUE self) {
diff --git a/ext/java/jar/jbson.jar b/ext/java/jar/jbson.jar
index 672589a..720fc27 100644
Binary files a/ext/java/jar/jbson.jar and b/ext/java/jar/jbson.jar differ
diff --git a/ext/java/src/org/jbson/RubyBSONEncoder.java b/ext/java/src/org/jbson/RubyBSONEncoder.java
index 9c4b06d..8dbd1b0 100644
--- a/ext/java/src/org/jbson/RubyBSONEncoder.java
+++ b/ext/java/src/org/jbson/RubyBSONEncoder.java
@@ -91,10 +91,11 @@ public class RubyBSONEncoder extends BSONEncoder {
         return _run.newFixnum(_max_bson_size);
     }
 
-    public static void update_max_bson_size(RubyObject obj, RubyObject conn) {
+    public static RubyFixnum update_max_bson_size(RubyObject obj, RubyObject conn) {
         Ruby _run = obj.getRuntime();
         _max_bson_size = ((Long)JavaEmbedUtils.invokeMethod( _run, conn, "max_bson_size",
           new Object[] {}, Object.class)).intValue();
+        return _run.newFixnum(_max_bson_size);
     }
 
     public RubyString encode( Object arg ) {
diff --git a/lib/bson.rb b/lib/bson.rb
index 556f568..b5b1910 100644
--- a/lib/bson.rb
+++ b/lib/bson.rb
@@ -6,11 +6,17 @@ MINIMUM_BSON_EXT_VERSION = "1.2.rc0"
 
 module BSON
   VERSION = "1.2.rc0"
+
+  if defined? Mongo
+    DEFAULT_MAX_BSON_SIZE = Mongo::DEFAULT_MAX_BSON_SIZE
+  else
+    DEFAULT_MAX_BSON_SIZE = 4 * 1024 * 1024
+  end
+
   def self.serialize(obj, check_keys=false, move_id=false)
     BSON_CODER.serialize(obj, check_keys, move_id)
   end
 
-
   def self.deserialize(buf=nil)
     BSON_CODER.deserialize(buf)
   end
diff --git a/test/bson/bson_test.rb b/test/bson/bson_test.rb
index c88c762..a7a8b75 100644
--- a/test/bson/bson_test.rb
+++ b/test/bson/bson_test.rb
@@ -78,6 +78,15 @@ class BSONTest < Test::Unit::TestCase
     assert BSON_CODER.max_bson_size >= BSON::DEFAULT_MAX_BSON_SIZE
   end
 
+  def test_update_max_bson_size
+    require 'ostruct'
+    mock_conn = OpenStruct.new
+    size      = 7 * 1024 * 1024
+    mock_conn.max_bson_size = size
+    assert_equal size, BSON_CODER.update_max_bson_size(mock_conn)
+    assert_equal size, BSON_CODER.max_bson_size
+  end
+
   def test_round_trip
     doc = {'doc' => 123}
     @encoder.deserialize(@encoder.serialize(doc))