diff --git a/block/io.c b/block/io.c
index 2592ca1bd4..4c797454a4 100644
--- a/block/io.c
+++ b/block/io.c
@@ -945,6 +945,8 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
     size_t skip_bytes;
     int ret;
 
+    assert(child->perm & (BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE));
+
     /* Cover entire cluster so no additional backing file I/O is required when
      * allocating cluster in the image file.
      */
@@ -1336,6 +1338,7 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child,
     assert(!waited || !req->serialising);
     assert(req->overlap_offset <= offset);
     assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
+    assert(child->perm & BLK_PERM_WRITE);
 
     ret = notifier_with_return_list_notify(&bs->before_write_notifiers, req);