diff --git a/README.md b/README.md
index 3eb87a0..167c6de 100644
--- a/README.md
+++ b/README.md
@@ -266,6 +266,12 @@ The statemachine will create for all states an `on_entry_` and `on_exit_` functi
 If the are not used, they will be optimized away by the compiler. An example be
 found in `on_entry_on_exit_generic`.
 
+### Transition callback
+
+The statemachine will call for every transition a transition callback. This function
+is called with both the old state and new state as arguments. An example can be found
+in `transition_callback`.
+
 ## Helpers
 
 ### Auto-derive certain traits for states and events
diff --git a/macros/src/codegen.rs b/macros/src/codegen.rs
index 6664a8b..dfef05b 100644
--- a/macros/src/codegen.rs
+++ b/macros/src/codegen.rs
@@ -490,8 +490,10 @@ pub fn generate_code(sm: &ParsedStateMachine) -> proc_macro2::TokenStream {
                                         if guard_result.map_err(#error_type_name::GuardFailed)? {
                                               #action_code
                                               let out_state = #states_type_name::#out_state;
+                                              let in_state = #states_type_name::#in_state;
                                               self.context.log_state_change(&out_state);
                                               #entry_exit_states
+                                              self.context().transition_callback(&in_state, &out_state);
                                               self.state = Some(out_state);
                                               return self.state()
                                         }
@@ -500,8 +502,10 @@ pub fn generate_code(sm: &ParsedStateMachine) -> proc_macro2::TokenStream {
                                     quote!{
                                        #action_code
                                        let out_state = #states_type_name::#out_state;
+                                       let in_state = #states_type_name::#in_state;
                                        self.context.log_state_change(&out_state);
                                        #entry_exit_states
+                                       self.context().transition_callback(&in_state, &out_state);
                                        self.state = Some(out_state);
                                        return self.state();
                                    }
@@ -609,6 +613,11 @@ pub fn generate_code(sm: &ParsedStateMachine) -> proc_macro2::TokenStream {
             /// `process_event()`. No-op by default but can be overridden in implementations
             /// of a state machine's `StateMachineContext` trait.
             fn log_state_change(&self, new_state: & #states_type_name) {}
+
+            /// Called when transitioning to a new state as a result of an event passed to
+            /// `process_event()`. No-op by default but can be overridden in implementations
+            /// of a state machine's `StateMachineContext` trait.
+            fn transition_callback(&self, old_state: & #states_type_name, new_state: & #states_type_name) {}
         }
 
         /// List of auto-generated states.
diff --git a/macros/src/parser/state_machine.rs b/macros/src/parser/state_machine.rs
index 85f4402..e44dc13 100644
--- a/macros/src/parser/state_machine.rs
+++ b/macros/src/parser/state_machine.rs
@@ -142,12 +142,12 @@ impl parse::Parse for StateMachine {
                     return Err(parse::Error::new(
                         input.span(),
                         format!(
-                            "Unknown keyword {}. Support keywords: [\"name\", \
-                                \"transitions\", \
-                                \"temporary_context\", \
-                                \"custom_guard_error\", \
-                                \"derive_states\", \
-                                \"derive_events\"
+                            "Unknown keyword {}. Support keywords: [\"name\",
+                                \"transitions\",
+                                \"temporary_context\",
+                                \"custom_guard_error\",
+                                \"derive_states\",
+                                \"derive_events\",
                                 ]",
                             keyword
                         ),