diff --git a/src/event_system.c b/src/event_system.c
index 6682b72..c1b3e16 100644
--- a/src/event_system.c
+++ b/src/event_system.c
@@ -131,19 +131,19 @@ void es_deinit(EventSystem *event_system) {
   event_system->id = 0;
 }
 
-Event es_register_event(EventSystem event_system) {
+Event es_register_event(EventSystem *event_system) {
   Event event = INVALID_EVENT;
 
-  if (IS_INVALID_SYSTEM(event_system)) {
+  if (!event_system || IS_INVALID_SYSTEM((*event_system))) {
     goto RETURN_EVENT;
   }
 
-  ESInternal *es = get_event_system_internal(event_system);
+  ESInternal *es = get_event_system_internal(*event_system);
   if (!VALID_MAGIC(es)) {
     goto RETURN_EVENT;
   }
 
-  event.system = event_system;
+  event.system = *event_system;
 
   EventSlot *event_slots_array = get_event_slots_array(es);
 
@@ -193,14 +193,14 @@ void es_deregister_event(EventSystem event_system, Event *event) {
   event->id = 0;
 }
 
-EventListener es_add_event_listener(EventSystem event_system, Event event, EventCallback callback) {
+EventListener es_add_event_listener(EventSystem *event_system, Event event, EventCallback callback) {
   EventListener listener = INVALID_LISTENER;
 
-  if (IS_INVALID_SYSTEM(event_system) || IS_INVALID_EVENT(event) || event_system.id != event.system.id || !callback) {
+  if (!event_system || IS_INVALID_SYSTEM((*event_system)) || IS_INVALID_EVENT(event) || event_system->id != event.system.id || !callback) {
     goto RETURN_LISTENER;
   }
 
-  ESInternal *es = get_event_system_internal(event_system);
+  ESInternal *es = get_event_system_internal(*event_system);
   if (!VALID_MAGIC(es)) {
     goto RETURN_LISTENER;
   }
diff --git a/src/event_system.h b/src/event_system.h
index a04ad74..c938699 100644
--- a/src/event_system.h
+++ b/src/event_system.h
@@ -30,8 +30,8 @@ typedef void (*EventCallback)(void *data);
 
 EventSystem   es_init(u64 initial_event_capacity, u64 initial_listeners_capacity);
 void          es_deinit(EventSystem *event_system);
-Event         es_register_event(EventSystem event_system);
+Event         es_register_event(EventSystem *event_system);
 void          es_deregister_event(EventSystem event_system, Event *event);
-EventListener es_add_event_listener(EventSystem event_system, Event event, EventCallback callback);
+EventListener es_add_event_listener(EventSystem *event_system, Event event, EventCallback callback);
 void          es_remove_event_listener(EventSystem event_system, EventListener listener);
 void          es_emit_event(EventSystem event_system, Event event, void *data);
diff --git a/src/main.c b/src/main.c
index 64a5771..3727218 100644
--- a/src/main.c
+++ b/src/main.c
@@ -40,8 +40,8 @@ int main(void) {
   EventSystem es = es_init(COUNT_EVENTS, 64);
 
   for (int i = 0; i < COUNT_EVENTS; ++i) {
-    events[i]    = es_register_event(es);
-    listeners[i] = es_add_event_listener(es, events[i], callbacks[i]);
+    events[i]    = es_register_event(&es);
+    listeners[i] = es_add_event_listener(&es, events[i], callbacks[i]);
   }
 
   WindowEvent   window_event   = { .window_width = 1280, .window_height = 720 };
@@ -61,8 +61,8 @@ int main(void) {
   es_emit_event(es, events[EVENT_MOUSE],    (void *)&mouse_event);
 
   // You can also add other events not stored in an array
-  Event         extra_event = es_register_event(es);
-  EventListener listener    = es_add_event_listener(es, extra_event, extra_event_handler);
+  Event         extra_event = es_register_event(&es);
+  EventListener listener    = es_add_event_listener(&es, extra_event, extra_event_handler);
   es_emit_event(es, extra_event, NULL);
   es_remove_event_listener(es, listener);
   es_deregister_event(es, &extra_event);