diff --git a/block/block-backend.c b/block/block-backend.c
index 39cd99df2b..12ef80ea17 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1540,7 +1540,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset,
                             QEMUIOVector *qiov, BdrvRequestFlags flags,
                             BlockCompletionFunc *cb, void *opaque)
 {
-    assert(qiov->size <= INT64_MAX);
+    assert((uint64_t)qiov->size <= INT64_MAX);
     return blk_aio_prwv(blk, offset, qiov->size, qiov,
                         blk_aio_write_entry, flags, cb, opaque);
 }