Voltage fault detection

[Manx]

5V tolerant inputs of STM32 have an additional requirement that Vin < (VCC + 3.6 V), so I have to protect the MCU against a situation when 3V3 is lost when 5V is still supplied. I want to make a circuit that would assert INHibit pin of the 5V SMPS (L5973D) when 3V3 fault occurs. My idea is the following:



R13 is for the situation when 3V3 fails as open circuit, R11 is for the situation when 3V3 gets shorted to ground. In any case, there will be more than 3.3V across the Zener diode, so the transistor will start conducting, thus making INH (volProbe1) HIGH.

Does this make sense? What I don't like (based on EasyEda simulations) is that it can be finicky concerning component values. R14 is what I guess the internal INH pullup could be. R12 has to be low enough that it overpowers the stupid internal pullup, and at the same time high enough that it can be overpowered by the transistor. I guess a Darlington would be better here. But anyways, does my idea make sense? Or am I trying to reinvent the wheel the hard way?