On Thursday, 27 April 2023 at 20:16:32 UTC, Walter Bright wrote: > Thanks! Every .h file we can make work makes ImportC that much > more useful. It's a high leverage activity for time invested. I filed one earlier today: https://issues.dlang.org/show_bug.cgi?id=23867 Seems to have an easy fix. I added #define __builtin_isnan isnan to the .c file and it compiled.