diff --git a/lib/mongo/collection.rb b/lib/mongo/collection.rb
index 9f9145d..78d426a 100644
--- a/lib/mongo/collection.rb
+++ b/lib/mongo/collection.rb
@@ -202,13 +202,7 @@ module Mongo
     def insert(doc_or_docs, options={})
       doc_or_docs = [doc_or_docs] unless doc_or_docs.is_a?(Array)
       doc_or_docs.collect! { |doc| @pk_factory.create_pk(doc) }
-      result = insert_documents(doc_or_docs)
-      if options.delete(:safe)
-        error = @db.error
-        if error
-          raise OperationFailure, error
-        end
-      end
+      result = insert_documents(doc_or_docs, @name, true, options[:safe])
       result.size > 1 ? result : result.first
     end
     alias_method :<<, :insert
@@ -259,11 +253,12 @@ module Mongo
       message.put_int(options[:upsert] ? 1 : 0) # 1 if a repsert operation (upsert)
       message.put_array(BSON.new.serialize(spec, false).to_a)
       message.put_array(BSON.new.serialize(document, false).to_a)
-      @db.send_message_with_operation(Mongo::Constants::OP_UPDATE, message, 
-        "db.#{@name}.update(#{spec.inspect}, #{document.inspect})")
-
-      if options[:safe] && error=@db.error
-        raise OperationFailure, error
+      if options[:safe]
+        @db.send_message_with_safe_check(Mongo::Constants::OP_UPDATE, message,
+          "db.#{@name}.update(#{spec.inspect}, #{document.inspect})")
+      else
+        @db.send_message_with_operation(Mongo::Constants::OP_UPDATE, message, 
+          "db.#{@name}.update(#{spec.inspect}, #{document.inspect})")
       end
     end
 
@@ -480,13 +475,18 @@ EOS
     # Sends an Mongo::Constants::OP_INSERT message to the database.
     # Takes an array of +documents+, an optional +collection_name+, and a
     # +check_keys+ setting.
-    def insert_documents(documents, collection_name=@name, check_keys=true)
+    def insert_documents(documents, collection_name=@name, check_keys=true, safe=false)
       message = ByteBuffer.new
       message.put_int(0)
       BSON.serialize_cstr(message, "#{@db.name}.#{collection_name}")
       documents.each { |doc| message.put_array(BSON.new.serialize(doc, check_keys).to_a) }
-      @db.send_message_with_operation(Mongo::Constants::OP_INSERT, message,
-        "db.#{collection_name}.insert(#{documents.inspect})")
+      if safe
+        @db.send_message_with_safe_check(Mongo::Constants::OP_INSERT, message,
+          "db.#{collection_name}.insert(#{documents.inspect})")
+      else
+        @db.send_message_with_operation(Mongo::Constants::OP_INSERT, message,
+          "db.#{collection_name}.insert(#{documents.inspect})")
+      end
       documents.collect { |o| o[:_id] || o['_id'] }
     end
 
diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index 5e9e5a0..0540984 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -450,6 +450,21 @@ module Mongo
       end
     end
 
+    # Sends a message to the database, waits for a response, and raises
+    # and exception if the operation has failed.
+    def send_message_with_safe_check(operation, message, log_message=nil)
+      message_with_headers = add_message_headers(operation, message)
+      message_with_check   = last_error_message
+      @logger.debug("  MONGODB #{log_message || message}") if @logger
+      @semaphore.synchronize do
+        send_message_on_socket(message_with_headers.append!(message_with_check).to_s)
+        docs, num_received, cursor_id = receive
+        if num_received == 1 && error = docs[0]['err']
+          raise Mongo::OperationFailure, error
+        end
+      end
+    end
+
     # Note: this method is a stub. Will be completed in an upcoming refactoring.
     def receive_message_with_operation(operation, message, log_message=nil)
       message_with_headers = add_message_headers(operation, message).to_s
@@ -512,10 +527,10 @@ module Mongo
     end
 
     # Sending a message on socket.
-    def send_message_on_socket(message_with_headers)
+    def send_message_on_socket(packed_message)
       connect_to_master if !connected? && @auto_reconnect
       begin
-        @socket.print(message_with_headers)
+        @socket.print(packed_message)
         @socket.flush
       rescue => ex
         close
@@ -583,10 +598,6 @@ module Mongo
       end
     end
 
-    def _synchronize &block
-      @semaphore.synchronize &block
-    end
-
     def full_collection_name(collection_name)
       "#{@name}.#{collection_name}"
     end
@@ -619,6 +630,35 @@ module Mongo
       @@current_request_id
     end
 
+    # Creates a getlasterror message.
+    def last_error_message
+      generate_last_error_message
+    end
+
+    def generate_last_error_message
+      message = ByteBuffer.new
+      message.put_int(0)
+      BSON.serialize_cstr(message, "#{@name}.$cmd")
+      message.put_int(0)
+      message.put_int(-1)
+      message.put_array(BSON.new.serialize({:getlasterror => 1}).to_a)
+      add_message_headers(Mongo::Constants::OP_QUERY, message)
+    end
+
+    def reset_error_message
+      @@reset_error_message ||= generate_reset_error_message
+    end
+
+    def generate_reset_error_message
+      message = ByteBuffer.new
+      message.put_int(0)
+      BSON.serialize_cstr(message, "#{@name}.$cmd")
+      message.put_int(0)
+      message.put_int(-1)
+      message.put_array(BSON.new.serialize({:reseterror => 1}).to_a)
+      add_message_headers(Mongo::Constants::OP_QUERY, message)
+    end
+
     def hash_password(username, plaintext)
       Digest::MD5.hexdigest("#{username}:mongo:#{plaintext}")
     end
diff --git a/test/test_threading.rb b/test/test_threading.rb
index 8d11b11..fb2a78c 100644
--- a/test/test_threading.rb
+++ b/test/test_threading.rb
@@ -1,18 +1,68 @@
-$LOAD_PATH[0,0] = File.join(File.dirname(__FILE__), '..', 'lib')
-require 'mongo'
-require 'test/unit'
+require 'test/test_helper'
 
 class TestThreading < Test::Unit::TestCase
 
   include Mongo
 
-  @@host = ENV['MONGO_RUBY_DRIVER_HOST'] || 'localhost'
-  @@port = ENV['MONGO_RUBY_DRIVER_PORT'] || Connection::DEFAULT_PORT
-  @@db = Connection.new(@@host, @@port).db('ruby-mongo-test')
+  @@db = Connection.new.db('ruby-mongo-test')
   @@coll = @@db.collection('thread-test-collection')
 
+  def set_up_safe_data
+    @@db.drop_collection('duplicate')
+    @@db.drop_collection('unique')
+    @duplicate = @@db.collection('duplicate')
+    @unique    = @@db.collection('unique') 
+
+    @duplicate.insert("test" => "insert")
+    @duplicate.insert("test" => "update")
+    @unique.insert("test" => "insert")
+    @unique.insert("test" => "update")
+    @unique.create_index("test", true)
+  end
+
+  def test_safe_update
+    set_up_safe_data
+    threads = []
+    100.times do |i|
+      threads[i] = Thread.new do
+        if i % 2 == 0
+          assert_raise Mongo::OperationFailure do
+            @unique.update({"test" => "insert"}, {"$set" => {"test" => "update"}}, :safe => true)
+          end
+        else
+          @duplicate.update({"test" => "insert"}, {"$set" => {"test" => "update"}}, :safe => true)
+        end
+      end
+    end
+  
+    100.times do |i|
+      threads[i].join
+    end
+  end
+
+  def test_safe_insert
+    set_up_safe_data
+    threads = []
+    100.times do |i|
+      threads[i] = Thread.new do
+        if i % 2 == 0
+          assert_raise Mongo::OperationFailure do
+            @unique.insert({"test" => "insert"}, :safe => true)
+          end
+        else
+          @duplicate.insert({"test" => "insert"}, :safe => true)
+        end
+      end
+    end
+  
+    100.times do |i|
+      threads[i].join
+    end
+  end
+
   def test_threading
-    @@coll.remove
+    @@coll.drop
+    @@coll = @@db.collection('thread-test-collection')
 
     1000.times do |i|
       @@coll.insert("x" => i)
@@ -21,13 +71,13 @@ class TestThreading < Test::Unit::TestCase
     threads = []
 
     10.times do |i|
-      threads[i] = Thread.new{
+      threads[i] = Thread.new do
         sum = 0
-        @@coll.find().each { |document|
+        @@coll.find().each do |document|
           sum += document["x"]
-        }
+        end
         assert_equal 499500, sum
-      }
+      end
     end
 
     10.times do |i|
diff --git a/test/unit/collection_test.rb b/test/unit/collection_test.rb
index cb1b792..da7506d 100644
--- a/test/unit/collection_test.rb
+++ b/test/unit/collection_test.rb
@@ -30,6 +30,25 @@ class CollectionTest < Test::Unit::TestCase
       end
       @coll.insert({:title => 'Moby Dick'})
     end
+
+    should "send safe update message" do
+      @db = MockDB.new("testing", ['localhost', 27017], :logger => @logger)
+      @coll = @db.collection('books')
+      @db.expects(:send_message_with_safe_check).with do |op, msg, log|
+        op == 2001 && log.include?("db.books.update")
+      end
+      @coll.update({}, {:title => 'Moby Dick'}, :safe => true)
+
+    end
+
+    should "send safe insert message" do
+      @db = MockDB.new("testing", ['localhost', 27017], :logger => @logger)
+      @coll = @db.collection('books')
+      @db.expects(:send_message_with_safe_check).with do |op, msg, log|
+        op == 2001 && log.include?("db.books.update")
+      end
+      @coll.update({}, {:title => 'Moby Dick'}, :safe => true)
+    end
   end
 end
 
diff --git a/test/unit/db_test.rb b/test/unit/db_test.rb
index 9e70da3..2622cbf 100644
--- a/test/unit/db_test.rb
+++ b/test/unit/db_test.rb
@@ -3,10 +3,22 @@ require 'test/test_helper'
 class DBTest < Test::Unit::TestCase
 
   class MockDB < DB
+    attr_accessor :socket
 
     def connect_to_master
       true
     end
+
+    public :add_message_headers
+  end
+
+  def insert_message(db, documents)
+    documents = [documents] unless documents.is_a?(Array)
+    message = ByteBuffer.new
+    message.put_int(0)
+    BSON.serialize_cstr(message, "#{db.name}.test")
+    documents.each { |doc| message.put_array(BSON.new.serialize(doc, true).to_a) }
+    message = db.add_message_headers(Mongo::Constants::OP_INSERT, message)
   end
 
   context "DB commands" do 
@@ -47,6 +59,24 @@ class DBTest < Test::Unit::TestCase
     end
   end
 
+  context "safe messages" do
+    setup do
+      @db = MockDB.new("testing", ['localhost', 27017])
+      @collection = mock()
+      @db.stubs(:system_command_collection).returns(@collection)
+    end
+
+    should "receive getlasterror message" do
+      @socket = mock()
+      @socket.stubs(:close)
+      @socket.expects(:flush)
+      @socket.expects(:print).with { |message| message.include?('getlasterror') }
+      @db.socket = @socket
+      @db.stubs(:receive)
+      message = insert_message(@db, {:a => 1})
+      @db.send_message_with_safe_check(Mongo::Constants::OP_QUERY, message)
+    end
+  end
 end