Check reCAPTCHA after updating to phpBB 3.3

I operate two phpBB forums that use reCAPTCHA during registration for spam prevention. I just updated them to phpBB 3.3, which switches from checkbox captcha to the newer(?) "invisible reCAPTCHA." The demo in the board settings, though, showed an error message about invisible reCAPTCHA not being enabled for the site key. That makes sense since I registered the sites with the v2 checkbox verification. To make the captcha work again, I had to reregister the sites with reCAPTCHA as the v2 invisible verification and get new keys.