diff --git a/sys/geom/geom_disk.c b/sys/geom/geom_disk.c
index d7fa43ab421..effc3b77331 100644
--- a/sys/geom/geom_disk.c
+++ b/sys/geom/geom_disk.c
@@ -657,6 +657,13 @@ disk_create(struct disk *dp, int version)
 		    dp->d_name, dp->d_unit);
 		return;
 	}
+	if (dp->d_flags & DISKFLAG_RESERVED) {
+		printf("WARNING: Attempt to add non-MPSAFE disk %s%d\n",
+		    dp->d_name, dp->d_unit);
+		printf("WARNING: Ignoring disk %s%d\n",
+		    dp->d_name, dp->d_unit);
+		return;
+	}
 	KASSERT(dp->d_strategy != NULL, ("disk_create need d_strategy"));
 	KASSERT(dp->d_name != NULL, ("disk_create need d_name"));
 	KASSERT(*dp->d_name != 0, ("disk_create need d_name"));
diff --git a/sys/geom/geom_disk.h b/sys/geom/geom_disk.h
index 3c983ee6e04..4cf53c4e5d0 100644
--- a/sys/geom/geom_disk.h
+++ b/sys/geom/geom_disk.h
@@ -103,6 +103,7 @@ struct disk {
 	void			*d_drv1;
 };
 
+#define DISKFLAG_RESERVED	0x1	/* Was NEEDSGIANT */
 #define DISKFLAG_OPEN		0x2
 #define DISKFLAG_CANDELETE	0x4
 #define DISKFLAG_CANFLUSHCACHE	0x8