diff --git a/expat/xmlwf/unixfilemap.c b/expat/xmlwf/unixfilemap.c
index 0cfd976b..02331c54 100644
--- a/expat/xmlwf/unixfilemap.c
+++ b/expat/xmlwf/unixfilemap.c
@@ -41,6 +41,7 @@
 #include <errno.h>
 #include <string.h>
 #include <stdio.h>
+#include <stdlib.h> // NULL
 #include <unistd.h>
 
 #ifndef MAP_FILE
@@ -93,7 +94,7 @@ filemap(const tchar *name,
     close(fd);
     return 1;
   }
-  p = mmap((void *)0, nbytes, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, (off_t)0);
+  p = mmap(NULL, nbytes, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, (off_t)0);
   if (p == (void *)-1) {
     tperror(name);
     close(fd);