diff --git a/block.c b/block.c
index 366999b15c067a33e204019ba0ec5bd8b1432afd..61795fea46401fe7677d82556ed54204e9fafb56 100644
--- a/block.c
+++ b/block.c
@@ -999,7 +999,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
     }
 
     /* backing files always opened read-only */
-    back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT);
+    back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT |
+                                    BDRV_O_COPY_ON_READ);
 
     ret = bdrv_open(bs->backing_hd,
                     *backing_filename ? backing_filename : NULL, options,