diff --git a/ChangeLog b/ChangeLog
index 378f6c025..34ce5df40 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,13 @@
 2016-03-04  Richard Frith-Macdonald <rfm@gnu.org>
 
 	* Source/NSCalendar.m: Fix 64bit issue with undefined components.
+	* Source\NSBundle.m:
+	* Source\NSFileManager.m:
+	* SSL\GSSSLHandle.m:
+	* Headers\GNUstepBase\GSConfig.h.in:
+	* macosx\GNUstepBase\preface.h:
+	Standardise on using _WIN32 and _WIN64 defines, following the
+	informal convention used by all the compilers we might be compiled with.
 
 2016-03-01  Richard Frith-Macdonald <rfm@gnu.org>
 
diff --git a/Headers/GNUstepBase/GSConfig.h.in b/Headers/GNUstepBase/GSConfig.h.in
index d1aae13fe..b4f9d038b 100644
--- a/Headers/GNUstepBase/GSConfig.h.in
+++ b/Headers/GNUstepBase/GSConfig.h.in
@@ -30,31 +30,25 @@
 #define	included_GSConfig_h
 
 /* Check the compiler to see if we are building on/for ms-windows.
- * Whatever the compiler uses, we want a standard setting of __WIN32__
- * for a windows build.
+ * Whatever the compiler uses, we want a standard setting of _WIN64
+ * to indicate 64bit AND _WIN32 to indicate ms-windows.
+ * These are defined by gcc, clang, and microsoft compilers anyway.
  */
 #if     defined(__WIN32__) \
-	|| defined(_WIN32) \
 	|| defined(__MS_WIN32__) \
-	|| defined(__MINGW64__)
-#  if	!defined(__WIN32__)
-#    define __WIN32__
+	|| defined(__MINGW32__)
+#  if	!defined(_WIN32)
+#    define _WIN32
 #  endif
 #endif
-
-/* Check the compiler to see if we are building on/for 64bit ms-windows.
- * Whatever the compiler uses, we want a standard setting of __WIN64__
- * to indicate 64bit AND __WIN32__ to indicate ms-windows.
- */
 #if     defined(__WIN64__) \
-	|| defined(_WIN64) \
 	|| defined(__MS_WIN64__) \
 	|| defined(__MINGW64__)
 #  if	!defined(__WIN64__)
 #    define __WIN64__
 #  endif
-#  if	!defined(__WIN32__)
-#    define __WIN32__
+#  if	!defined(_WIN32)
+#    define _WIN32
 #  endif
 #endif
 
@@ -310,7 +304,7 @@ typedef	struct {
 #  define __has_extension(x) __has_feature(x)
 #endif
 
-#if defined(__WIN32__)
+#if defined(_WIN32)
 #define BOOL WinBOOL
 #include <w32api.h>
 #ifndef _WIN32_WINNT
@@ -336,7 +330,7 @@ typedef	struct {
 #  include <objc/block_runtime.h>
 #endif
 
-#ifndef __WIN32__
+#ifndef _WIN32
 #include <sys/param.h> /* Hack to get rid of warning in GNU libc 2.0.3. */
 #endif
 
diff --git a/SSL/GSSSLHandle.m b/SSL/GSSSLHandle.m
index 7640b6e7e..fc9318585 100644
--- a/SSL/GSSSLHandle.m
+++ b/SSL/GSSSLHandle.m
@@ -25,19 +25,13 @@
 
 #include "config.h"
 
-#if     defined(__WIN32__) || defined(_WIN32) || defined(__MS_WIN32__)
-#ifndef __WIN32__
-#define __WIN32__
+#if     defined(__WIN32__) || defined(__MINGW32__) || defined(__MS_WIN32__)
+#ifndef _WIN32
+#define _WIN32
 #endif
 #endif
 
-#ifdef __MINGW__
-#ifndef __WIN32__
-#define __WIN32__
-#endif
-#endif
-
-#if defined(__WIN32__)
+#if defined(_WIN32)
 #include <windows.h>
 #endif
 
diff --git a/Source/NSBundle.m b/Source/NSBundle.m
index 03a13c931..228ff7519 100644
--- a/Source/NSBundle.m
+++ b/Source/NSBundle.m
@@ -301,7 +301,7 @@ AbsolutePathOfExecutable(NSString *path, BOOL atLaunch)
 	      result = [prefix stringByStandardizingPath];
 	      break;
 	    }
-#if defined(__WIN32__)
+#if defined(_WIN32)
 	  else
 	    {
 	      NSString	*extension = [path pathExtension];
@@ -1348,7 +1348,7 @@ _bundle_load_callback(Class theClass, struct objc_category *theCategory)
          the executable name here - just in case it turns out it's a
          tool.  */
       NSString *toolName = [GSPrivateExecutablePath() lastPathComponent];
-#if defined(__WIN32__) || defined(__CYGWIN__)
+#if defined(_WIN32) || defined(__CYGWIN__)
       toolName = [toolName stringByDeletingPathExtension];
 #endif
 
diff --git a/Source/NSFileManager.m b/Source/NSFileManager.m
index cdf6462b0..b6a0fe913 100644
--- a/Source/NSFileManager.m
+++ b/Source/NSFileManager.m
@@ -92,7 +92,7 @@
 
 /* determine filesystem max path length */
 
-#if defined(_POSIX_VERSION) || defined(__WIN32__)
+#if defined(_POSIX_VERSION) || defined(_WIN32)
 # if defined(__MINGW__)
 #   include <sys/utime.h>
 # else
@@ -549,7 +549,7 @@ static NSStringEncoding	defaultEncoding;
       BOOL		ok = NO;
       struct _STATB	sb;
 
-#if  defined(__WIN32__) || defined(_POSIX_VERSION)
+#if  defined(_WIN32) || defined(_POSIX_VERSION)
       struct _UTIMB ub;
 #else
       time_t ub[2];
@@ -559,7 +559,7 @@ static NSStringEncoding	defaultEncoding;
 	{
 	  ok = NO;
 	}
-#if  defined(__WIN32__)
+#if  defined(_WIN32)
       else if (sb.st_mode & _S_IFDIR)
 	{
 	  ok = YES;	// Directories don't have modification times.
@@ -567,7 +567,7 @@ static NSStringEncoding	defaultEncoding;
 #endif
       else
 	{
-#if  defined(__WIN32__) || defined(_POSIX_VERSION)
+#if  defined(_WIN32) || defined(_POSIX_VERSION)
 	  ub.actime = sb.st_atime;
 	  ub.modtime = [date timeIntervalSince1970];
 	  ok = (_UTIME(lpath, &ub) == 0);
diff --git a/macosx/GNUstepBase/preface.h b/macosx/GNUstepBase/preface.h
index 81381d451..0dc5fd112 100644
--- a/macosx/GNUstepBase/preface.h
+++ b/macosx/GNUstepBase/preface.h
@@ -28,26 +28,6 @@
 #include <stdarg.h>
 #include <GNUstepBase/objc-gnu2next.h>
 
-#if     defined(__WIN32__) || defined(_WIN32) || defined(__MS_WIN32__)
-#ifndef __WIN32__
-#define __WIN32__
-#endif
-#endif
-
-#ifdef __MINGW32__
-#ifndef __MINGW__
-#define __MINGW__
-#endif
-#ifndef __WIN32__
-#define __WIN32__
-#endif
-#endif
-
-#if defined(__WIN32__)
-#include <windows.h>
-#define GNUSTEP_BASE_SOCKET_MESSAGE (WM_USER + 1)
-#endif
-
 #if NeXT_RUNTIME
  #include <objc/objc.h>
  #include <objc/objc-class.h>
@@ -86,9 +66,7 @@
 #define	_C_ULNG_LNG	'Q'
 #endif
 
-#ifndef __WIN32__
 #include <sys/param.h> /* Hack to get rid of warning in GNU libc 2.0.3. */
-#endif
 
 /* The following group of lines maintained by the gstep-base configure */
 #define GNUSTEP_BASE_VERSION            @VERSION@