diff --git a/lib/mongo/collection.rb b/lib/mongo/collection.rb
index 9d2c54c..7e63fa0 100644
--- a/lib/mongo/collection.rb
+++ b/lib/mongo/collection.rb
@@ -77,6 +77,7 @@ module XGen
         def save(object)
           if id = object[:_id] || object['_id']
             repsert({:_id => id}, object)
+            id
           else
             insert(object)
           end
diff --git a/tests/test_db_api.rb b/tests/test_db_api.rb
index 39b8f5e..18d6ada 100644
--- a/tests/test_db_api.rb
+++ b/tests/test_db_api.rb
@@ -48,7 +48,7 @@ class DBAPITest < Test::Unit::TestCase
 
   def test_insert_multiple
     ids = @@coll.insert({'a' => 2}, {'b' => 3})
-    
+
     ids.each do |i|
       assert_kind_of ObjectID, i
     end
@@ -619,10 +619,11 @@ class DBAPITest < Test::Unit::TestCase
 
     a = {"hello" => "world"}
 
-    assert_kind_of ObjectID, @@coll.save(a)
+    id = @@coll.save(a)
+    assert_kind_of ObjectID, id
     assert_equal 1, @@coll.count
 
-    @@coll.save(@@coll.find_first)
+    assert_equal id, @@coll.save(@@coll.find_first)
     assert_equal 1, @@coll.count
 
     assert_equal "world", @@coll.find_first()["hello"]