diff --git a/events/UserAllocatedEvent.h b/events/UserAllocatedEvent.h
index 71c4b700cb..f8f17dcf1e 100644
--- a/events/UserAllocatedEvent.h
+++ b/events/UserAllocatedEvent.h
@@ -215,6 +215,7 @@ public:
      */
     void delay(int delay)
     {
+        MBED_ASSERT(!_post_ref);
         equeue_event_delay(&_e + 1, delay);
     }
 
@@ -224,6 +225,7 @@ public:
      */
     void period(int period)
     {
+        MBED_ASSERT(!_post_ref);
         equeue_event_period(&_e + 1, period);
     }