SQL Group By with an Order By

Question

I have a table of tags and want to get the highest count tags from the list.

Sample data looks like this

id (1) tag ('night')
id (2) tag ('awesome')
id (3) tag ('night')

using

SELECT COUNT(*), `Tag` from `images-tags`
GROUP BY `Tag`

gets me back the data I'm looking for perfectly. However, I would like to organize it, so that the highest tag counts are first, and limit it to only send me the first 20 or so.

I tried this...

SELECT COUNT(id), `Tag` from `images-tags`
GROUP BY `Tag`
ORDER BY COUNT(id) DESC
LIMIT 20

and I keep getting an "Invalid use of group function - ErrNr 1111"

What am I doing wrong?