diff --git a/sim_fio.c b/sim_fio.c
index 16018cb4..e6a96089 100644
--- a/sim_fio.c
+++ b/sim_fio.c
@@ -334,7 +334,7 @@ return (t_offset)(ftello64 (st));
 
 /* Apple OS/X */
 
-#if defined (__APPLE__) || defined (__FreeBSD__) || defined(__NetBSD__) || defined (__OpenBSD__) 
+#if defined (__APPLE__) || defined (__FreeBSD__) || defined(__NetBSD__) || defined (__OpenBSD__) || defined (__CYGWIN__) 
 #define S_SIM_IO_FSEEK_EXT_ 1
 int sim_fseeko (FILE *st, t_offset xpos, int origin) 
 {
diff --git a/sim_fio.h b/sim_fio.h
index 9dbc035f..01ee0791 100644
--- a/sim_fio.h
+++ b/sim_fio.h
@@ -38,10 +38,10 @@
 #define fxwrite(a,b,c,d)        sim_fwrite (a, b, c, d)
 
 int32 sim_finit (void);
-#if (defined (__linux) || defined (__linux__) || defined (__hpux) || defined (_AIX) ||                           \
+#if (defined (__linux) || defined (__linux__) || defined (__hpux) || defined (_AIX) ||         \
      (defined (VMS) && (defined (__ALPHA) || defined (__ia64)) && (__DECC_VER >= 60590001)) || \
      ((defined(__sun) || defined(__sun__)) && defined(_LARGEFILE_SOURCE)) ||                   \
-     defined (_WIN32) || defined (__APPLE__) ||                                                \
+     defined (_WIN32) || defined (__APPLE__) || defined (__CYGWIN__) ||                        \
      defined (__FreeBSD__) || defined(__NetBSD__) || defined (__OpenBSD__)) && !defined (DONT_DO_LARGEFILE)
 typedef t_int64        t_offset;
 #else