Weird error in MYSQL

Trick source

I got this trying to calculate the standard deviation of a dataset:

mysql> select STDEV_SAMP(precipitation_av) from p_year_averages where lon='-6.25' and lat='35.05';
   ERROR 1548 (HY000): Cannot load from mysql.proc. The table is probably corrupted

Googling a bit, it seems that the fix is simple. In Ubuntu:

$ sudo mysql_upgrade -u root -p

It will ask your system password, then your Mysql password. Then the problem is gone.