diff --git a/lib/process_shared.rb b/lib/process_shared.rb
index 1d625d6..2ef9257 100644
--- a/lib/process_shared.rb
+++ b/lib/process_shared.rb
@@ -28,4 +28,5 @@ end
 require 'process_shared/binary_semaphore'
 require 'process_shared/mutex'
 require 'process_shared/condition_variable'
+require 'process_shared/monitor'
 
diff --git a/lib/process_shared/monitor.rb b/lib/process_shared/monitor.rb
new file mode 100644
index 0000000..51ea44a
--- /dev/null
+++ b/lib/process_shared/monitor.rb
@@ -0,0 +1,31 @@
+require 'process_shared'
+require 'process_shared/mutex'
+
+module ProcessShared
+  class Monitor < Mutex
+    def initialize
+      super
+      @lock_count = 0
+    end
+
+    def lock
+      if locked_by == ::Process.pid
+        @lock_count += 1
+      else
+        super
+      end
+    end
+
+    def unlock
+      if locked_by == ::Process.pid
+        if @lock_count > 0
+          @lock_count -= 1
+        else
+          super
+        end
+      else
+        super
+      end
+    end
+  end
+end
diff --git a/lib/process_shared/mutex.rb b/lib/process_shared/mutex.rb
index 6de5d12..1aab1ed 100644
--- a/lib/process_shared/mutex.rb
+++ b/lib/process_shared/mutex.rb
@@ -94,7 +94,7 @@ module ProcessShared
       end
     end
 
-    private
+    protected
 
     def locked_by
       with_internal_lock do
diff --git a/spec/process_shared/monitor_spec.rb b/spec/process_shared/monitor_spec.rb
new file mode 100644
index 0000000..e62b3d6
--- /dev/null
+++ b/spec/process_shared/monitor_spec.rb
@@ -0,0 +1,34 @@
+require 'spec_helper'
+require 'process_shared'
+
+module ProcessShared
+  describe Monitor do
+
+    include LockBehavior
+
+    before :each do
+      @lock = Monitor.new
+    end
+
+    it 'raises exception when unlocked by other process' do
+      pid = Kernel.fork do
+        @lock.lock
+        sleep 0.2
+        @lock.unlock
+        Kernel.exit!
+      end
+
+      sleep 0.1
+      proc { @lock.unlock }.must_raise(ProcessError)
+
+      ::Process.wait(pid)
+    end
+
+    it 'raises nothing with nested lock' do
+      @lock.lock
+      @lock.lock
+      @lock.unlock
+      @lock.unlock
+    end
+  end
+end