diff --git a/lib/micromachine.rb b/lib/micromachine.rb
index bc09755..72f475c 100644
--- a/lib/micromachine.rb
+++ b/lib/micromachine.rb
@@ -3,9 +3,11 @@ class MicroMachine
   InvalidState = Class.new(ArgumentError)
 
   attr_reader :transitions_for
+  attr_reader :previous_state
   attr_reader :state
 
   def initialize(initial_state)
+    @previous_state = nil
     @state = initial_state
     @transitions_for = Hash.new
     @callbacks = Hash.new { |hash, key| hash[key] = [] }
@@ -20,7 +22,7 @@ def when(event, transitions)
   end
 
   def trigger(event)
-    trigger?(event) and change(event)
+    trigger?(event) and change(event) and notify(event)
   end
 
   def trigger!(event)
@@ -42,9 +44,13 @@ def states
   end
 
 private
-
   def change(event)
+    @previous_state = @state
     @state = transitions_for[event][@state]
+    true
+  end
+
+  def notify(event)
     callbacks = @callbacks[@state] + @callbacks[:any]
     callbacks.each { |callback| callback.call(event) }
     true
diff --git a/test/transitions.rb b/test/transitions.rb
index b131972..b99cd1e 100644
--- a/test/transitions.rb
+++ b/test/transitions.rb
@@ -12,6 +12,7 @@
 
 test "defines initial state" do |machine|
   assert_equal :pending, machine.state
+  assert_equal nil, machine.previous_state
 end
 
 test "raises an error if an invalid event is triggered" do |machine|
@@ -24,26 +25,32 @@
   assert !machine.trigger?(:reset)
   assert !machine.trigger(:reset)
   assert_equal :pending, machine.state
+  assert_equal nil, machine.previous_state
 end
 
 test "changes the state if transition is possible" do |machine|
   assert machine.trigger?(:confirm)
   assert machine.trigger(:confirm)
   assert_equal :confirmed, machine.state
+  assert_equal :pending, machine.previous_state
 end
 
 test "discerns multiple transitions" do |machine|
   machine.trigger(:confirm)
   assert_equal :confirmed, machine.state
+  assert_equal :pending, machine.previous_state
 
   machine.trigger(:reset)
   assert_equal :pending, machine.state
+  assert_equal :confirmed, machine.previous_state
 
   machine.trigger(:ignore)
   assert_equal :ignored, machine.state
+  assert_equal :pending, machine.previous_state
 
   machine.trigger(:reset)
   assert_equal :pending, machine.state
+  assert_equal :ignored, machine.previous_state
 end
 
 test "raises an error if event is triggered from/to a non complatible state" do |machine|