diff --git a/README.md b/README.md
index b787d01..0ca4f9a 100644
--- a/README.md
+++ b/README.md
@@ -10,9 +10,14 @@ Recurring jobs for [Sidekiq](http://mperham.github.com/sidekiq/).
 Sidetiq provides a simple API for defining recurring workers for Sidekiq.
 
 - Flexible DSL based on [ice_cube](http://seejohnrun.github.com/ice_cube/)
+
 - High-resolution timer using `clock_gettime(3)` (or `mach_absolute_time()` on
   Apple Mac OS X), allowing for accurate sub-second clock ticks.
 
+- Sidetiq uses a locking mechanism (based on `setnx` and `pexpire`) internally
+  so Sidetiq clocks can run in each Sidekiq process without interfering with
+  each other.
+
 ## DEPENDENCIES
 
 - [Sidekiq](http://mperham.github.com/sidekiq/)
@@ -38,8 +43,8 @@ class MyWorker
   include Sidekiq::Worker
   include Sidetiq::Schedulable
 
-  # Every other month on the first monday and last tuesday at 12 o'clock.
-  tiq { monthly(2).day_of_week(1 => [1], 2 => [-1]).hour_of_day(12) }
+  # Daily at midnight
+  tiq { daily }
 end
 ```
 
@@ -60,6 +65,18 @@ class MyWorker
 end
 ```
 
+Or complex schedules:
+
+```ruby
+class MyWorker
+  include Sidekiq::Worker
+  include Sidetiq::Schedulable
+
+  # Every other month on the first monday and last tuesday at 12 o'clock.
+  tiq { monthly(2).day_of_week(1 => [1], 2 => [-1]).hour_of_day(12) }
+end
+```
+
 The first time the tiq method is called, Sidetiq will automatically spin up
 it's clock thread and enqueue jobs for their next occurrence using
 `#perform_at`. Note that by default Sidekiq only polls every 15 seconds.
@@ -90,12 +107,6 @@ require 'sidetiq/web'
 
 ![Screenshot](http://f.cl.ly/items/1P2u1v091F3V1n381g2I/Screen%20Shot%202013-02-01%20at%2012.16.17.png)
 
-## CONSIDERATIONS
-
-If workers are spread across multiple machines multiple jobs might be enqueued
-at the same time. This can be avoided by using a locking library for Sidekiq,
-such as [sidekiq-unique-jobs](https://github.com/form26/sidekiq-unique-jobs).
-
 ## CONTRIBUTE
 
 If you'd like to contribute to Sidetiq, start by forking my repo on GitHub:
diff --git a/lib/sidetiq/clock.rb b/lib/sidetiq/clock.rb
index 20089ce..eb79268 100644
--- a/lib/sidetiq/clock.rb
+++ b/lib/sidetiq/clock.rb
@@ -1,13 +1,16 @@
 module Sidetiq
   configure do |config|
     config.priority = Thread.main.priority
-    config.resolution = 0.2
+    config.resolution = 1
+    config.lock_expire = 1000
   end
 
   class Clock
     include Singleton
     include MonitorMixin
 
+    START_TIME = Time.local(2010, 1, 1)
+
     attr_reader :schedules
 
     def initialize
@@ -17,18 +20,15 @@ module Sidetiq
     end
 
     def schedule_for(worker)
-      schedules[worker] ||= Sidetiq::Schedule.new
+      schedules[worker] ||= Sidetiq::Schedule.new(START_TIME)
     end
 
     def tick
       @tick = gettime
-
       synchronize do
         schedules.each do |worker, schedule|
           if schedule.schedule_next?(@tick)
-            occurrence = schedule.next_occurrence
-            Sidekiq.logger.info "Sidetiq::Clock enqueue #{worker.name} (at: #{occurrence.to_s})"
-            worker.perform_at(occurrence)
+            enqueue(worker, schedule.next_occurrence(@tick))
           end
         end
       end
@@ -36,6 +36,35 @@ module Sidetiq
 
     private
 
+    def enqueue(worker, time)
+      key = "sidetiq:#{worker.name}"
+
+      synchronize_clockworks("#{key}:lock") do |redis|
+        status = redis.get(key)
+
+        if status.nil? || status.to_f < time.to_f
+          time_f = time.to_f
+          Sidekiq.logger.info "Sidetiq::Clock enqueue #{worker.name} (at: #{time_f})"
+          redis.set(key, time_f)
+          worker.perform_at(time)
+        end
+      end
+    end
+
+    def synchronize_clockworks(lock)
+      Sidekiq.redis do |redis|
+        if redis.setnx(lock, 1)
+          Sidekiq.logger.debug "Sidetiq::Clock lock #{lock} #{Thread.current.inspect}"
+
+          redis.pexpire(lock, Sidetiq.config.lock_expire)
+          yield redis
+          redis.del(lock)
+
+          Sidekiq.logger.debug "Sidetiq::Clock unlock #{lock} #{Thread.current.inspect}"
+        end
+      end
+    end
+
     def start!
       Sidekiq.logger.info "Sidetiq::Clock start"
       thr = Thread.start { clock { tick } }
diff --git a/test/helper.rb b/test/helper.rb
index 70cdb2e..e731f2b 100644
--- a/test/helper.rb
+++ b/test/helper.rb
@@ -4,6 +4,7 @@ SimpleCov.start { add_filter "/test/" }
 require 'minitest/autorun'
 require 'mocha/setup'
 require 'rack/test'
+require 'mock_redis'
 
 require 'sidekiq'
 require 'sidekiq/testing'
@@ -20,3 +21,10 @@ end
 
 # Keep the test output clean
 Sidekiq.logger = Logger.new(nil)
+
+class Sidetiq::TestCase < MiniTest::Unit::TestCase
+  def setup
+    Sidekiq.redis { |r| r.flushall }
+  end
+end
+
diff --git a/test/test_clock.rb b/test/test_clock.rb
index e0dfdbd..d5804e2 100644
--- a/test/test_clock.rb
+++ b/test/test_clock.rb
@@ -1,12 +1,37 @@
 require_relative 'helper'
 
-class TestClock < MiniTest::Unit::TestCase
+class TestClock < Sidetiq::TestCase
+  def clock
+    @clock ||= Sidetiq::Clock.instance
+  end
+
   def test_gettime_seconds
-    assert_equal Sidetiq::Clock.instance.gettime.tv_sec, Time.now.tv_sec
+    assert_equal clock.gettime.tv_sec, Time.now.tv_sec
   end
 
   def test_gettime_nsec
-    refute_nil Sidetiq::Clock.instance.gettime.tv_nsec
+    refute_nil clock.gettime.tv_nsec
+  end
+
+  class FakeWorker; end
+
+  def test_enqueues_jobs_by_schedule
+    schedule = Sidetiq::Schedule.new(Sidetiq::Clock::START_TIME)
+    schedule.daily
+
+    clock.stubs(:schedules).returns(FakeWorker => schedule)
+
+    FakeWorker.expects(:perform_at).times(10)
+
+    10.times do |i|
+      clock.stubs(:gettime).returns(Time.local(2011, 1, i + 1, 1))
+      clock.tick
+    end
+
+    clock.stubs(:gettime).returns(Time.local(2011, 1, 10, 2))
+    clock.tick
+    clock.tick
+    clock.tick
   end
 end
 
diff --git a/test/test_config.rb b/test/test_config.rb
index 0de0129..936230d 100644
--- a/test/test_config.rb
+++ b/test/test_config.rb
@@ -1,6 +1,6 @@
 require_relative 'helper'
 
-class TestConfig < MiniTest::Unit::TestCase
+class TestConfig < Sidetiq::TestCase
   def setup
     @saved = Sidetiq.config
     Sidetiq.config = OpenStruct.new
diff --git a/test/test_errors.rb b/test/test_errors.rb
index 6768c34..a8c919b 100644
--- a/test/test_errors.rb
+++ b/test/test_errors.rb
@@ -1,6 +1,6 @@
 require_relative 'helper'
 
-class TestErrors < MiniTest::Unit::TestCase
+class TestErrors < Sidetiq::TestCase
   def test_error_superclass
     assert_equal StandardError, Sidetiq::Error.superclass
   end
diff --git a/test/test_schedule.rb b/test/test_schedule.rb
index c7651e6..4880233 100644
--- a/test/test_schedule.rb
+++ b/test/test_schedule.rb
@@ -1,6 +1,6 @@
 require_relative 'helper'
 
-class TestSchedule < MiniTest::Unit::TestCase
+class TestSchedule < Sidetiq::TestCase
   def test_super
     assert_equal IceCube::Schedule, Sidetiq::Schedule.superclass
   end
diff --git a/test/test_sidetiq.rb b/test/test_sidetiq.rb
deleted file mode 100644
index 36c8c21..0000000
--- a/test/test_sidetiq.rb
+++ /dev/null
@@ -1,37 +0,0 @@
-require_relative 'helper'
-
-class TestSidetiq < MiniTest::Unit::TestCase
-  class Worker
-    include Sidekiq::Worker
-    include Sidetiq::Schedulable
-
-    tiq do
-      daily.hour_of_day(0)
-    end
-  end
-
-  def clock
-    @clock ||= Sidetiq::Clock.instance
-  end
-
-  def tick
-    clock.tick
-  end
-
-  def test_scheduling
-    assert_equal 0, Worker.jobs.size # sanity
-
-    clock.stubs(:gettime).returns(Time.now + (24 * 60 * 60))
-    tick
-    assert_equal 1, Worker.jobs.size
-
-    clock.stubs(:gettime).returns(Time.now + (2 * 24 * 60 * 60))
-    tick
-    assert_equal 2, Worker.jobs.size
-
-    clock.stubs(:gettime).returns(Time.now + (2 * 24 * 60 * 60 + 1))
-    tick
-    assert_equal 2, Worker.jobs.size
-  end
-end
-
diff --git a/test/test_version.rb b/test/test_version.rb
index 58b3b50..7d8d33b 100644
--- a/test/test_version.rb
+++ b/test/test_version.rb
@@ -1,6 +1,6 @@
 require_relative 'helper'
 
-class TestVersion < MiniTest::Unit::TestCase
+class TestVersion < Sidetiq::TestCase
   def test_major
     assert_instance_of Fixnum, Sidetiq::VERSION::MAJOR
   end
diff --git a/test/test_web.rb b/test/test_web.rb
index a7a32c2..a339daf 100644
--- a/test/test_web.rb
+++ b/test/test_web.rb
@@ -1,6 +1,6 @@
 require_relative 'helper'
 
-class TestWeb < MiniTest::Unit::TestCase
+class TestWeb < Sidetiq::TestCase
   include Rack::Test::Methods
 
   class Worker