Question about how best to limit input voltage to opamp

I have an application where the input can be as high as 21VDC; I want
to do a non-inverting stage, powered by 24VDC with a gain < 1 to bring
it within a 3.3V range before feeding it to an ADC whose rail is tied
to 3.3VDC. By selecting the right gain resistors, the ADC should
never see a voltage greater than 3.3VDC, but I want to put in more
protection in case something happens and the ouput of the opamp stage
swings the input to the ADC beyond 3.3VDC and destroys the ADC.
One possible way that I've seen it done is to tie the output of the
opamp gain stage to the anode of a diode whose cathode is tied to
3.3VDC. Please confirm if this is a good way of doing this, any
caveats I should be aware of or if there are any other ideas you can
think of.
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I would put a simple zener across the input to be protected.
Reply to
Tim Perry

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