stored procedure outvars not looked up in execute immediate

CREATE PROCEDURE `getMax`(IN `cTable` VARCHAR(255), IN `cColumn` VARCHAR(255), OUT nMax INT) DETERMINISTIC

EXECUTE IMMEDIATE CONCAT('SELECT MAX(', cColumn, ') INTO nMax FROM ', cTable);

Query OK, 0 rows affected (0.001 sec)

call getMax('seq_1_to_100', 'seq', @max);

ERROR 1327 (42000): Undeclared variable: nMax