diff --git a/include/geos/gconst.h b/include/geos/gconst.h
index e70eb9304..3e42feed7 100644
--- a/include/geos/gconst.h
+++ b/include/geos/gconst.h
@@ -4,13 +4,15 @@
   reassembled by Maciej 'YTM/Elysium' Witkowiak
 */
 
-/* Here are constants which didn't fit into any other cathegory... */
+/* Here are constants which didn't fit into any other category... */
 
 #ifndef _GCONST_H
 #define _GCONST_H
 
-#define NULL            0
-#define FALSE           NULL
+#ifndef NULL
+#define NULL            ((void *) 0)
+#endif
+#define FALSE           0
 #define TRUE            0xff
 #define MOUSE_SPRNUM    0
 #define DISK_DRV_LGH    0x0d80
diff --git a/include/locale.h b/include/locale.h
index 3f23e01d2..f408e1ef3 100644
--- a/include/locale.h
+++ b/include/locale.h
@@ -39,9 +39,8 @@
 
 
 /* NULL pointer */
-#ifndef _HAVE_NULL
-#define NULL    0
-#define _HAVE_NULL
+#ifndef NULL
+#define NULL ((void *) 0)
 #endif
 
 /* Locale information constants */
@@ -82,6 +81,3 @@ char* __fastcall__ setlocale (int category, const char* locale);
 
 /* End of locale.h */
 #endif
-
-
-
diff --git a/include/stddef.h b/include/stddef.h
index ca93edf62..d2bfd6138 100644
--- a/include/stddef.h
+++ b/include/stddef.h
@@ -53,9 +53,8 @@ typedef unsigned size_t;
 #endif
 
 /* NULL pointer */
-#ifndef _HAVE_NULL
-#define NULL    ((void *) 0)
-#define _HAVE_NULL
+#ifndef NULL
+#define NULL ((void *) 0)
 #endif
 
 /* offsetof macro */
@@ -65,6 +64,3 @@ typedef unsigned size_t;
 
 /* End of stddef.h */
 #endif
-
-
-
diff --git a/include/stdio.h b/include/stdio.h
index 858dd5059..012b8e2ba 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -38,9 +38,8 @@
 
 
 /* NULL pointer */
-#ifndef _HAVE_NULL
-#define NULL    0
-#define _HAVE_NULL
+#ifndef NULL
+#define NULL ((void *) 0)
 #endif
 
 /* size_t is needed */
diff --git a/include/stdlib.h b/include/stdlib.h
index 4e7ffbd6a..e789f732b 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -44,6 +44,11 @@ typedef unsigned size_t;
 #define _HAVE_size_t
 #endif
 
+/* NULL pointer */
+#ifndef NULL
+#define NULL ((void *) 0)
+#endif
+
 /* Standard exit codes */
 #define EXIT_SUCCESS    0
 #define EXIT_FAILURE    1
@@ -167,6 +172,3 @@ int __fastcall__ putenv (char* s);
 
 /* End of stdlib.h */
 #endif
-
-
-
diff --git a/include/string.h b/include/string.h
index 854359dad..abaf80e7d 100644
--- a/include/string.h
+++ b/include/string.h
@@ -37,9 +37,8 @@
 #define _STRING_H
 
 /* NULL pointer */
-#ifndef _HAVE_NULL
-#define NULL    0
-#define _HAVE_NULL
+#ifndef NULL
+#define NULL ((void *) 0)
 #endif
 
 /* size_t is needed */
diff --git a/include/time.h b/include/time.h
index 642d68c4e..bfc2ac435 100644
--- a/include/time.h
+++ b/include/time.h
@@ -39,9 +39,8 @@
 
 
 /* NULL pointer */
-#ifndef _HAVE_NULL
-#define NULL    0
-#define _HAVE_NULL
+#ifndef NULL
+#define NULL ((void *) 0)
 #endif
 
 /* size_t is needed */
diff --git a/test/val/add4.c b/test/val/add4.c
index f02a7fb9c..2371aea69 100644
--- a/test/val/add4.c
+++ b/test/val/add4.c
@@ -22,7 +22,6 @@ long long0 = 0;
 long long1 = 0;
 unsigned long ulong0 = 0;
 unsigned long ulong1 = 0;
-#define NULL 0
 char *cP0=NULL;
 char *cP1=NULL;
 int *iP0=NULL;