The previous definition was: #define NUM(field_name) (sizeof(Maxwell3D::Regs::field_name) / sizeof(u32)) In cases where `field_name` happens to refer to an array, Clang thinks `sizeof(an array value) / sizeof(a type)` is an instance of the idiom where `sizeof` is used to compute an array length. So it thinks the type in the denominator ought to be the array element type, and warns if it isn't, assuming this is a mistake. In reality, `NUM` is not used to get array lengths at all, so there is no mistake. Silence the warning by applying Clang's suggested workaround of parenthesizing the denominator.