Hi!
I totally agree with the previous poster, "if ain't broken, don't fix it". If your lo seems fine and happy throughout the day and wakes happy from both, the day and naps, then he's probably getting the amount of sleep he needs, no matter what the "guide lines" say.
If you're hesistant about it, you might want to try an earlier nap time. You don't mention what time of the day his nap is, but probably he's having too much awake time before it and that might be the reason why the nap is short. With toddlers every reason is the opposite of what we think and overtiredness generally comes in the form of short or broken sleep. If an earlier nap is not happening you still have two options, which could be an earlier bedtime or trying to extend wake up time at least for 30 more mins. You'd be surprised to find out the advantages of an earlier bedtime, and as funny as it sounds, it sometimes helps lo sleep for longer nights.
Maybe the key here is provide more sleep chances for your lo and see if this can buy extra ZZZ's time. HTH and keep us posted!