diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
index a426e4e2acdac1fee2e341ba011e557cfeb5db95..7c9f4d79bdbc502f61ebd18901f313228ef17098 100644
--- a/fs/nilfs2/btree.c
+++ b/fs/nilfs2/btree.c
@@ -350,7 +350,7 @@ static int nilfs_btree_node_broken(const struct nilfs_btree_node *node,
 	if (unlikely(level < NILFS_BTREE_LEVEL_NODE_MIN ||
 		     level >= NILFS_BTREE_LEVEL_MAX ||
 		     (flags & NILFS_BTREE_NODE_ROOT) ||
-		     nchildren < 0 ||
+		     nchildren <= 0 ||
 		     nchildren > NILFS_BTREE_NODE_NCHILDREN_MAX(size))) {
 		nilfs_crit(inode->i_sb,
 			   "bad btree node (ino=%lu, blocknr=%llu): level = %d, flags = 0x%x, nchildren = %d",
@@ -381,7 +381,8 @@ static int nilfs_btree_root_broken(const struct nilfs_btree_node *node,
 	if (unlikely(level < NILFS_BTREE_LEVEL_NODE_MIN ||
 		     level >= NILFS_BTREE_LEVEL_MAX ||
 		     nchildren < 0 ||
-		     nchildren > NILFS_BTREE_ROOT_NCHILDREN_MAX)) {
+		     nchildren > NILFS_BTREE_ROOT_NCHILDREN_MAX ||
+		     (nchildren == 0 && level > NILFS_BTREE_LEVEL_NODE_MIN))) {
 		nilfs_crit(inode->i_sb,
 			   "bad btree root (ino=%lu): level = %d, flags = 0x%x, nchildren = %d",
 			   inode->i_ino, level, flags, nchildren);
@@ -1659,13 +1660,16 @@ static int nilfs_btree_check_delete(struct nilfs_bmap *btree, __u64 key)
 	int nchildren, ret;
 
 	root = nilfs_btree_get_root(btree);
+	nchildren = nilfs_btree_node_get_nchildren(root);
+	if (unlikely(nchildren == 0))
+		return 0;
+
 	switch (nilfs_btree_height(btree)) {
 	case 2:
 		bh = NULL;
 		node = root;
 		break;
 	case 3:
-		nchildren = nilfs_btree_node_get_nchildren(root);
 		if (nchildren > 1)
 			return 0;
 		ptr = nilfs_btree_node_get_ptr(root, nchildren - 1,
@@ -1674,12 +1678,12 @@ static int nilfs_btree_check_delete(struct nilfs_bmap *btree, __u64 key)
 		if (ret < 0)
 			return ret;
 		node = (struct nilfs_btree_node *)bh->b_data;
+		nchildren = nilfs_btree_node_get_nchildren(node);
 		break;
 	default:
 		return 0;
 	}
 
-	nchildren = nilfs_btree_node_get_nchildren(node);
 	maxkey = nilfs_btree_node_get_key(node, nchildren - 1);
 	nextmaxkey = (nchildren > 1) ?
 		nilfs_btree_node_get_key(node, nchildren - 2) : 0;