Why the ます形 of おっしゃる is おっしゃいます?


I'm studying for the N4 of the JLPT and in the 尊敬語 lesson is the verb おっしゃる

おっしゃる is the respectful form of 言う. When in the textbook they change the verb
to the ます形 it changes in a way that I can not understand.

How I understand it should be

> おっしゃる ► Ends in "る" so the "い" sound of that character is "り" ► おっしゃり ► and
> then we add the ます ► **おっしゃります**

How it is in the textbook:

> おっしゃる ► おっしゃいます

The same happens with

> くださる ► くださいます
>
> なさる ► なさいます
>
> いらっしゃる ► いらっしゃいます

Does someone knows why it is like this?




Simple enough, 仰有る【おっしゃる】/ 仰る 【おっしゃる】 is an irregular verb :) there is a bit
more irregular verbs in Japanese than the classicals する or 来る。

There is a nice [list of irregular
verbs](https://en.wikipedia.org/wiki/Japanese_irregular_verbs) on Wikipedia

