diff --git a/kernel-shared/extent-tree.c b/kernel-shared/extent-tree.c
index 92d5c521..0b0c40af 100644
--- a/kernel-shared/extent-tree.c
+++ b/kernel-shared/extent-tree.c
@@ -3529,6 +3529,12 @@ static int __btrfs_record_file_extent(struct btrfs_trans_handle *trans,
 	u64 extent_offset;
 	u64 num_bytes = *ret_num_bytes;
 
+	/*
+	 * @objectid should be an inode number, thus it must not be smaller
+	 * than BTRFS_FIRST_FREE_OBJECTID.
+	 */
+	ASSERT(objectid >= BTRFS_FIRST_FREE_OBJECTID);
+
 	/*
 	 * All supported file system should not use its 0 extent.
 	 * As it's for hole
diff --git a/mkfs/rootdir.c b/mkfs/rootdir.c
index 6b67a9b9..2cf6eef9 100644
--- a/mkfs/rootdir.c
+++ b/mkfs/rootdir.c
@@ -530,7 +530,13 @@ static int traverse_directory(struct btrfs_trans_handle *trans,
 				goto fail;
 			}
 
-			cur_inum = st.st_ino;
+			/*
+			 * We can not directly use the source ino number,
+			 * as there is a chance that the ino is smaller than
+			 * BTRFS_FIRST_FREE_OBJECTID, which will screw up
+			 * backref code.
+			 */
+			cur_inum = st.st_ino + BTRFS_FIRST_FREE_OBJECTID;
 			ret = add_directory_items(trans, root,
 						  cur_inum, parent_inum,
 						  cur_file->d_name,