diff --git a/hal/api/Callback.h b/hal/api/Callback.h
index fa1f5ecc3f..d7b4d12ec8 100644
--- a/hal/api/Callback.h
+++ b/hal/api/Callback.h
@@ -796,6 +796,9 @@ public:
     /** Call the attached function
      */
     R call() {
+        if (NULL == _thunk) {
+            return (R)0;
+        }
         return _thunk(_obj, &_func);
     }