System.QueryException: Invalid bind expression type of X for column of type Id

This piece of code:

    bindMap.put('idList', excludeIds);
    whereClause += (hasWhere ? ' and ' : ' where ') + ' Id NOT IN (:idList) ';

was generating this exception:

System.QueryException: Invalid bind expression type of Set for column of type Id

Which seemed... odd. excludeIds is declared as having type Set<Id> so why the error? After trying several variations of lists and sets, and casting before putting the value into the map to be doubly sure of it's type, I found the solution, remove the parentheses:

    bindMap.put('idList', excludeIds);
    whereClause += (hasWhere ? ' and ' : ' where ') + ' Id NOT IN :idList ';

Job done.