diff --git a/src/ic-cdk/src/api/call.rs b/src/ic-cdk/src/api/call.rs
index c335e459f..b437b30a2 100644
--- a/src/ic-cdk/src/api/call.rs
+++ b/src/ic-cdk/src/api/call.rs
@@ -153,6 +153,8 @@ unsafe extern "C" fn callback<T: AsRef<[u8]>>(state_ptr: *const RwLock<CallFutur
             // borrow_mut() the state as well. So we need to be careful to not double-borrow_mut.
             waker.wake()
         }
+    } else {
+        crate::trap("Call already trapped");
     }
 }