I discovered that the proof of a fundamental proposition in my maths PhD thesis had a mistake in it two weeks before my viva, after I had submitted. Not sure if

I discovered that the proof of a fundamental proposition in my maths PhD thesis had a mistake in it two weeks before my viva, after I had submitted. Not sure if that was a better or worse time to discover it! After a rather stressful few days, I managed to reprove it and took the correct proof along to the viva. The examiners were 'well, the result was obviously correct so we weren't worried about it'!