diff --git a/block.c b/block.c
index e4396a6..48528fd 100644
--- a/block.c
+++ b/block.c
@@ -649,12 +649,13 @@
     bs->opaque = g_malloc0(drv->instance_size);
 
     bs->enable_write_cache = !!(flags & BDRV_O_CACHE_WB);
+    open_flags = flags | BDRV_O_CACHE_WB;
 
     /*
      * Clear flags that are internal to the block layer before opening the
      * image.
      */
-    open_flags = flags & ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
+    open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
 
     /*
      * Snapshots should be writable.