diff --git a/arch/sim/src/Makefile b/arch/sim/src/Makefile
index 5e49b0ff04..808388410a 100644
--- a/arch/sim/src/Makefile
+++ b/arch/sim/src/Makefile
@@ -46,8 +46,6 @@ else
 endif
 else
   USEX = n
-  CFLAGS += -DCYGWIN
-  HOSTCFLAGS += -DCYGWIN
 endif
 
 CFLAGS += -I$(TOPDIR)/sched
diff --git a/arch/sim/src/up_internal.h b/arch/sim/src/up_internal.h
index 094776390f..82df76e1f1 100644
--- a/arch/sim/src/up_internal.h
+++ b/arch/sim/src/up_internal.h
@@ -128,7 +128,7 @@ extern unsigned long up_getwalltime( void );
 
 /* up_tapdev.c ************************************************************/
 
-#if defined(CONFIG_NET) && !defined(CYGWIN)
+#if defined(CONFIG_NET) && !defined(__CYGWIN__)
 extern void tapdev_init(void);
 extern unsigned int tapdev_read(unsigned char *buf, unsigned int buflen);
 extern void tapdev_send(unsigned char *buf, unsigned int buflen);
@@ -140,7 +140,7 @@ extern void tapdev_send(unsigned char *buf, unsigned int buflen);
 
 /* up_wpcap.c *************************************************************/
 
-#if defined(CONFIG_NET) && defined(CYGWIN)
+#if defined(CONFIG_NET) && defined(__CYGWIN__)
 extern void wpcap_init(void);
 extern unsigned int wpcap_read(unsigned char *buf, unsigned int buflen);
 extern void wpcap_send(unsigned char *buf, unsigned int buflen);
diff --git a/arch/sim/src/up_tapdev.c b/arch/sim/src/up_tapdev.c
index 9c88245b18..4176258e2f 100644
--- a/arch/sim/src/up_tapdev.c
+++ b/arch/sim/src/up_tapdev.c
@@ -38,7 +38,7 @@
  *
  ****************************************************************************/
 
-#ifndef CYGWIN
+#ifndef __CYGWIN__
 
 /****************************************************************************
  * Included Files
@@ -266,6 +266,6 @@ void tapdev_send(unsigned char *buf, unsigned int buflen)
   dump_ethhdr("write", buf, buflen);
 }
 
-#endif /* !CYGWIN */
+#endif /* !__CYGWIN__ */
 
 
diff --git a/arch/sim/src/up_wpcap.c b/arch/sim/src/up_wpcap.c
index 9fd9e50647..18a6ad4aec 100644
--- a/arch/sim/src/up_wpcap.c
+++ b/arch/sim/src/up_wpcap.c
@@ -38,7 +38,7 @@
  *
  ****************************************************************************/
 
-#ifdef CYGWIN
+#ifdef __CYGWIN__
 
 /****************************************************************************
  * Included Files
@@ -309,4 +309,4 @@ void wpcap_send(unsigned char *buf, unsigned int buflen)
     }
 }
 
-#endif /* CYGWIN */
+#endif /* __CYGWIN__ */