CONCAT in Trigger

CREATE TRIGGER set_aka_name
BEFORE INSERT ON sandbox_person
FOR EACH ROW
BEGIN
  IF (NEW.aka IS NULL) THEN
    NEW.aka = CONCAT(NEW.fname, ' ', NEW.lname);
  END IF;
END

## Throwing this ERROR:  #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.aka = CONCAT(NEW.fname, ' ', NEW.lname)' at line 6