diff --git a/include/hsm/details/sm.h b/include/hsm/details/sm.h
index 7d7d78d..d38d53c 100644
--- a/include/hsm/details/sm.h
+++ b/include/hsm/details/sm.h
@@ -77,7 +77,7 @@ template <class RootState, class... OptionalParameters> class sm {
         update_current_regions();
     }
 
-    template <class Event> auto process_event(Event&& event)
+    template <class Event> auto process_event(Event&& event) -> bool
     {
         static_assert(
             bh::contains(
@@ -87,10 +87,11 @@ template <class RootState, class... OptionalParameters> class sm {
 
         if (!process_event_internal(event)) {
             call_unexpected_event_handler(event);
-            return;
+            return false;
         }
 
         process_deferred_events();
+        return true;
     }
 
     template <class State> auto is(State state) -> bool
diff --git a/test/integration/unexpected_event_handler.cpp b/test/integration/unexpected_event_handler.cpp
index 6731994..7e33608 100644
--- a/test/integration/unexpected_event_handler.cpp
+++ b/test/integration/unexpected_event_handler.cpp
@@ -63,7 +63,7 @@ class UnexpectedEventHandler : public Test {
 TEST_F(UnexpectedEventHandler, should_call_unexpected_event_handler)
 {
     auto event = e2 {};
-    sm.process_event(event);
+    ASSERT_FALSE(sm.process_event(event));
 
     ASSERT_TRUE(event.called);
 }
@@ -71,10 +71,10 @@ TEST_F(UnexpectedEventHandler, should_call_unexpected_event_handler)
 TEST_F(UnexpectedEventHandler, should_not_call_unexpected_event_handler_when_guard_fails)
 {
 
-    sm.process_event(e3 {});
+    ASSERT_TRUE(sm.process_event(e3 {}));
 
     auto event = e2 {};
-    sm.process_event(event);
+    ASSERT_TRUE(sm.process_event(event));
 
     ASSERT_FALSE(event.called);
 }
\ No newline at end of file