Index: sys/dev/proto/proto_core.c
===================================================================
--- sys/dev/proto/proto_core.c
+++ sys/dev/proto/proto_core.c
@@ -78,7 +78,7 @@
 
 struct cdevsw proto_devsw = {
        .d_version = D_VERSION,
-   .d_flags = 0,
+   .d_flags = D_NEEDGIANT,
        .d_name = proto_driver_name,
        .d_open = proto_open,
        .d_close = proto_close,