Why is KeyValuePair <int, long> 16 bytes?

Question

KeyValuePair<int, int>:    8 bytes
KeyValuePair<long, long>: 16 bytes
KeyValuePair<long, int>:  16 bytes (!!)
KeyValuePair<int, long>:  16 bytes (!!)

I would expect the last two pairs to only require 8 (long) + 4 (int)= 12 bytes. Why do they occupy 16?

Sizes were determined using dynamic SizeOf emitted through ILGenerator, as discussed here: Size of the overall structure

Answer 1

This is due to alignment of the data structure . To quote a Wikipedia article:

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