diff --git a/Makefile b/Makefile
index 14ee038..8c506de 100644
--- a/Makefile
+++ b/Makefile
@@ -25,15 +25,15 @@ WARNINGS=-pedantic -Wall -Wextra -Wstrict-prototypes -Wno-unused-parameter
 CFLAGS=-O2 $(WARNINGS)
 LDFLAGS=-s
 LIBS=-lcurses
-DEFINES=-DAUTOCONF -DPROGRAM=$(PROGRAM) # -DNDEBUG
-ifeq ($(uname_S),Linux)
- DEFINES += -DPOSIX -DUSG
-else ifeq ($(uname_S),CYGWIN)
- DEFINES += -DCYGWIN -DSYSV
-else ifeq ($(uname_S),MSYS)
- DEFINES += -DCYGWIN -DSYSV
-else ifeq ($(uname_S),NetBSD)
- DEFINES += -DPOSIX -DBSD=1
+DEFINES=-DAUTOCONF -DPROGRAM=$(PROGRAM) -D_GNU_SOURCE # -DNDEBUG
+ifeq ($(uname_S),Linux)			# __unix__ __linux__
+ DEFINES += -DUSG -DPOSIX
+else ifeq ($(uname_S),CYGWIN)	# __unix__ __CYGWIN__
+ DEFINES += -DSYSV # -DPOSIX
+else ifeq ($(uname_S),MSYS)		# __unix__ __CYGWIN__ __MSYS__
+ DEFINES += -DSYSV # -DPOSIX
+else ifeq ($(uname_S),NetBSD)	# __unix__ __NetBSD__
+ DEFINES += -DBSD=1 -DPOSIX
 else
  $(error $(uname_S) needs configuration)
 endif
diff --git a/posix.c b/posix.c
index 29b1a37..75c80a2 100644
--- a/posix.c
+++ b/posix.c
@@ -1,18 +1,16 @@
 /* posix.c -- posix implementation of termio.h */
-#ifdef POSIX
-
 #include "termio.h"
 
-/*	posix.c
- *
- *      The functions in this file negotiate with the operating system for
- *      characters, and write characters in a barely buffered fashion on the
- *      display. All operating systems.
- *
- *	modified by Petri Kutvonen
- *
- *	based on termio.c, with all the old cruft removed, and
- *	fixed for termios rather than the old termio.. Linus Torvalds
+#ifdef POSIX
+
+/* The functions in this file negotiate with the operating system for
+   characters, and write characters in a barely buffered fashion on the
+   display.  All operating systems.
+
+   modified by Petri Kutvonen
+ 
+   based on termio.c, with all the old cruft removed, and
+   fixed for termios rather than the old termio.. Linus Torvalds
  */
 
 #include <errno.h>
@@ -38,7 +36,7 @@ int ttcol = HUGE ;		/* Column location of HW cursor */
 #define XCASE 0000004
 #endif
 
-#ifdef CYGWIN
+#ifdef __CYGWIN__			/* gcc predefined (see cpp -dM) */
 #define XCASE 0
 #define ECHOPRT 0
 #define PENDIN 0
@@ -247,8 +245,6 @@ int typahead(void)
 	return x;
 }
 
-#else
-typedef void _pedantic_empty_translation_unit ;
-#endif              /* not POSIX */
+#endif
 
 /* end of posix.c */
diff --git a/termio.c b/termio.c
index f17265e..e306cf2 100644
--- a/termio.c
+++ b/termio.c
@@ -1,15 +1,13 @@
 /* termio.c -- implements termio.h */
-#if !defined( POSIX)
-
 #include "termio.h"
 
-/*  TERMIO.C
- *
- * The functions in this file negotiate with the operating system for
- * characters, and write characters in a barely buffered fashion on the display.
- * All operating systems.
- *
- *  modified by Petri Kutvonen
+#ifndef POSIX
+
+/* The functions in this file negotiate with the operating system for
+   characters, and write characters in a barely buffered fashion on the
+   display.  All operating systems.
+
+   modified by Petri Kutvonen
  */
 
 #include <stdio.h>
@@ -258,14 +256,12 @@ int typahead( void)
     return kbdqp;
 #endif
 
-#if !UNIX
+#  if !UNIX
     return FALSE;
-#endif
+#  endif
 }
-#endif
+# endif
 
-#else
-typedef void _pedantic_empty_translation_unit ;
 #endif              /* not POSIX */
 
 /* end of termio.c */
diff --git a/utf8.c b/utf8.c
index 0531fba..d7cfcd7 100644
--- a/utf8.c
+++ b/utf8.c
@@ -1,16 +1,13 @@
 /* utf8.c -- implements utf8.h, conversion between unicode and UTF-8 */
 #include "utf8.h"
 
-#define _XOPEN_SOURCE   /* wcwidth in wchar.h */
-
 #include <assert.h>
-#include <wchar.h>
+#include <wchar.h>					/* either _XOPEN_SOURCE or _GNU_SOURCE */
 
 
 /* Display width of UTF-8 character */
 int _utf8_width( unicode_t c) {
-#if CYGWIN
-    assert( sizeof( wchar_t) == 2) ;    /* wcwidth only supports UTF-16 */
+#if __SIZEOF_WCHAR_T__ == 2		    /* wcwidth only supports UTF-16 */
     return (c < 0x10000) ? wcwidth( (wchar_t) c) : -1 ;
 #else
     return wcwidth( (wchar_t) c) ;