diff --git a/src/task.c b/src/task.c
index 47f44456..977e66f9 100644
--- a/src/task.c
+++ b/src/task.c
@@ -1068,7 +1068,7 @@ promiseid_t tf_task_allocate_promise(tf_task_t* task)
 	promiseid_t promiseId;
 	do {
 		promiseId = task->_nextPromise++;
-	} while (_tf_task_find_promise(task, promiseId));
+	} while (_tf_task_find_promise(task, promiseId) || !promiseId);
 
 	promise_t promise =
 	{