It must have the same width as unsigned char in that scenario, but that does not make it unsigned char. § 6.5 of C11 only allows casting to "a character type" (

It must have the same width as unsigned char in that scenario, but that does not make it unsigned char. § 6.5 of C11 only allows casting to "a character type" (and a few cases irrelevant in this context), not "a type of CHAR_BITS width". There's no requirement that uint8_t is a typedef for unsigned char.