diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index bb51dbb..160c71a 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -475,9 +475,13 @@ module XGen
               objects.collect! { |o|
                 @pk_factory.create_pk(o)
               }
+            else
+              objects = objects.collect do |o|
+                o[:_id] || o['_id'] ? o : o.merge(:_id => ObjectID.new)
+              end
             end
             send_to_db(InsertMessage.new(@name, collection_name, true, *objects))
-            objects
+            objects.collect { |o| o[:_id] || o['_id'] }
           }
         end
 
diff --git a/tests/test_db.rb b/tests/test_db.rb
index 09d327a..68a13f6 100644
--- a/tests/test_db.rb
+++ b/tests/test_db.rb
@@ -66,19 +66,20 @@ class DBTest < Test::Unit::TestCase
     coll = db.collection('test')
     coll.clear
 
+    insert_id = coll.insert('name' => 'Fred', 'age' => 42)
     # new id gets added to returned object
-    obj = coll.insert('name' => 'Fred', 'age' => 42)
     row = coll.find_first({'name' => 'Fred'}, :limit => 1)
     oid = row['_id']
     assert_not_nil oid
-    assert_equal obj, row
+    assert_equal insert_id, oid
 
     oid = XGen::Mongo::Driver::ObjectID.new
-    obj = coll.insert('_id' => oid, 'name' => 'Barney', 'age' => 41)
-    row = coll.find_first({'name' => 'Barney'}, :limit => 1)
+    data = {'_id' => oid, 'name' => 'Barney', 'age' => 41}
+    coll.insert(data)
+    row = coll.find_first({'name' => data['name']}, :limit => 1)
     db_oid = row['_id']
     assert_equal oid, db_oid
-    assert_equal obj, row
+    assert_equal data, row
 
     coll.clear
   end
diff --git a/tests/test_db_api.rb b/tests/test_db_api.rb
index b00eaa0..39b8f5e 100644
--- a/tests/test_db_api.rb
+++ b/tests/test_db_api.rb
@@ -13,7 +13,8 @@ class DBAPITest < Test::Unit::TestCase
 
   def setup
     @@coll.clear
-    @r1 = @@coll.insert('a' => 1) # collection not created until it's used
+    @r1 = {'a' => 1}
+    @@coll.insert(@r1) # collection not created until it's used
     @@coll_full_name = 'ruby-mongo-test.test'
   end
 
@@ -29,8 +30,8 @@ class DBAPITest < Test::Unit::TestCase
   end
 
   def test_insert
-    @@coll.insert('a' => 2)
-    @@coll.insert('b' => 3)
+    assert_kind_of ObjectID, @@coll.insert('a' => 2)
+    assert_kind_of ObjectID, @@coll.insert('b' => 3)
 
     assert_equal 3, @@coll.count
     docs = @@coll.find().to_a
@@ -46,7 +47,11 @@ class DBAPITest < Test::Unit::TestCase
   end
 
   def test_insert_multiple
-    @@coll.insert({'a' => 2}, {'b' => 3})
+    ids = @@coll.insert({'a' => 2}, {'b' => 3})
+    
+    ids.each do |i|
+      assert_kind_of ObjectID, i
+    end
 
     assert_equal 3, @@coll.count
     docs = @@coll.find().to_a
@@ -614,7 +619,7 @@ class DBAPITest < Test::Unit::TestCase
 
     a = {"hello" => "world"}
 
-    @@coll.save(a)
+    assert_kind_of ObjectID, @@coll.save(a)
     assert_equal 1, @@coll.count
 
     @@coll.save(@@coll.find_first)