OK, can somebody suggest why this returns "Msg 102, Level 15, State 1, Line 4 Incorrect syntax near '='." on my 9.0.4207 SQL server?

declare @i tinyint

SELECT @i = 0

while @i < 255

SELECT @i+=1

SELECT @i

Msg 102, Level 15, State 1, Line 4

Incorrect syntax near '='.