Include <ctype.h> for isxdigit(3). diff -u -r ../poppler-0.59.0/poppler/Form.cc ./poppler/Form.cc --- ../poppler-0.59.0/poppler/Form.cc 2017-08-16 00:16:09.000000000 +0200 +++ ./poppler/Form.cc 2017-09-11 20:06:45.434163003 +0200 @@ -29,6 +29,7 @@ #include <set> #include <limits> +#include <ctype.h> #include <stddef.h> #include <string.h> #include "goo/gmem.h"