diff --git a/block/vmdk.c b/block/vmdk.c
index 8dec6ef767..de8cb859f8 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -397,6 +397,8 @@ static int vmdk_parent_open(BlockDriverState *bs)
         pstrcpy(bs->auto_backing_file, end_name - p_name + 1, p_name);
         pstrcpy(bs->backing_file, sizeof(bs->backing_file),
                 bs->auto_backing_file);
+        pstrcpy(bs->backing_format, sizeof(bs->backing_format),
+                "vmdk");
     }
 
 out: