Compile error in linux but not in windows - expected unqualified-id before '/'

Hi all,

I'm looking for some help in resolving a compile issue I'm encountering in Linux but not in Windows.
Version of Arduino I'm using is 1.8.7, and the error I'm getting is this:

simpleDSTadjust.h:19:25: error: expected unqualified-id before '/' token
#define weekday(t) (((t / SECS_PER_DAY) + 4) % 7)

The file is from a github repo, and I've made sure the same set of libraries are used in both Windows and Linux. I've tried everything I can think of with no luck, I'd appreciate any thoughts.

Thanks.

If you post your program I will try to compile it on my Linux laptop.

...R