--- flex-2.6.4/src/flexdef.h.orig	Thu Jan 23 22:38:30 2020
+++ flex-2.6.4/src/flexdef.h	Thu Jan 23 22:38:45 2020
@@ -72,7 +72,7 @@
 #include <stdbool.h>
 #include <stdarg.h>
 /* Required: regcomp(), regexec() and regerror() in <regex.h> */
-#include <regex.h>
+#include <pcre2posix.h>
 /* Required: strcasecmp() in <strings.h> */
 #include <strings.h>
 #include "flexint.h"