diff -ruN nqc-3.1.r6-old/compiler/lexer.cpp nqc-3.1.r6-new/compiler/lexer.cpp
--- nqc-3.1.r6-old/compiler/lexer.cpp	2007-06-06 20:19:10.000000000 +0200
+++ nqc-3.1.r6-new/compiler/lexer.cpp	2022-10-13 07:57:08.247213954 +0200
@@ -11,6 +11,7 @@
 #define YY_FLEX_MINOR_VERSION 5
 
 #include <stdio.h>
+#include <unistd.h>
 
 #if defined(__MWERKS__) && !__MACH__ && !YY_NEVER_INTERACTIVE
 #include <unix.h>