A user/An user??

[potplant]

I am currently reading a document written by a foreign colleague (ie learnt English very formally, usually excellent grammar)and he has written 'an user does .....' which doesn't sound right.

I have changed it to "a user...".

Is this an expection to the vowel rule or is he technically right but my version is accepted norm?

I think it's an exception because of the sound - although it's a vowel it sounds like "a yoo-zer", not like e.g. "an umbrella"

It's a user. Phonetically, it begins with a consonant.