diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 6a0e8ef664c1..d2488b7e54a5 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -599,7 +599,7 @@ static void udf_do_extend_final_block(struct inode *inode,
 	 */
 	if (new_elen <= (last_ext->extLength & UDF_EXTENT_LENGTH_MASK))
 		return;
-	added_bytes = (last_ext->extLength & UDF_EXTENT_LENGTH_MASK) - new_elen;
+	added_bytes = new_elen - (last_ext->extLength & UDF_EXTENT_LENGTH_MASK);
 	last_ext->extLength += added_bytes;
 	UDF_I(inode)->i_lenExtents += added_bytes;