diff --git a/sys/fs/nullfs/null_subr.c b/sys/fs/nullfs/null_subr.c
index cccbe51b294..7a2d7524471 100644
--- a/sys/fs/nullfs/null_subr.c
+++ b/sys/fs/nullfs/null_subr.c
@@ -304,9 +304,8 @@ null_hashrem(xp)
 }
 
 #ifdef DIAGNOSTIC
-#include "opt_ddb.h"
 
-#ifdef DDB
+#ifdef KDB
 #define	null_checkvp_barrier	1
 #else
 #define	null_checkvp_barrier	0
diff --git a/sys/fs/nullfs/null_vfsops.c b/sys/fs/nullfs/null_vfsops.c
index 9014c74b474..0ecfda23818 100644
--- a/sys/fs/nullfs/null_vfsops.c
+++ b/sys/fs/nullfs/null_vfsops.c
@@ -42,6 +42,7 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/kdb.h>
 #include <sys/kernel.h>
 #include <sys/lock.h>
 #include <sys/malloc.h>
@@ -260,7 +261,7 @@ nullfs_root(mp, vpp)
 
 #ifdef NULLFS_DEBUG
 	if (VOP_ISLOCKED(vp, NULL)) {
-		Debugger("root vnode is locked.\n");
+		kdb_enter("root vnode is locked.\n");
 		vrele(vp);
 		return (EDEADLK);
 	}