Incorrect value for str_to_date

I'm running a simple procedure that reads from a VARCHAR column and inserts data into a TIME column, using this format: STR_TO_DATE(vTestTime, '%H:%i'). I'm getting the error >SQL Error (1411): Incorrect datetime value: '09:22' for function str_to_date I find that a similar statement, SELECT STR_TO_DATE("09:22", "%H:%i") gives me a NULL when I run it from a HeidiSQL client. I'm sure this syntax used to work and I'm not aware of having changed any settings, can you suggest what I've done wrong? Edit: Just remembered I have made a recent change, I installed a Wordpress database on the same server, might that have had some affect? Here's what get running on the server: mysql> select str_to_date("09:22", "%H:%i"); +-------------------------------+ | str_to_date("09:22", "%H:%i") | +-------------------------------+ | NULL | +-------------------------------+ 1 row in set, 1 warning (0.00 sec) Warning (Code 1411): Incorrect datetime value: '09:22' for function str_to_date