diff --git a/block/qcow2.c b/block/qcow2.c
index ebad4e1..0ce7150 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -338,7 +338,7 @@
 
 static void qcow_aio_cancel(BlockDriverAIOCB *blockacb)
 {
-    QCowAIOCB *acb = (QCowAIOCB *)blockacb;
+    QCowAIOCB *acb = container_of(blockacb, QCowAIOCB, common);
     if (acb->hd_aiocb)
         bdrv_aio_cancel(acb->hd_aiocb);
     qemu_aio_release(acb);