--- a/netwerk/base/nsURLHelper.h
+++ b/netwerk/base/nsURLHelper.h
@@ -216,17 +216,17 @@ void net_ParseContentType(const nsACStri
                           nsACString       &aContentCharset,
                           bool             *aHadCharset,
                           int32_t          *aCharsetStart,
                           int32_t          *aCharsetEnd);
 
 /* inline versions */
 
 /* remember the 64-bit platforms ;-) */
-#define NET_MAX_ADDRESS (((char*)0)-1)
+#define NET_MAX_ADDRESS ((char*)UINTPTR_MAX)
 
 inline char *net_FindCharInSet(const char *str, const char *set)
 {
     return net_FindCharInSet(str, NET_MAX_ADDRESS, set);
 }
 inline char *net_FindCharNotInSet(const char *str, const char *set)
 {
     return net_FindCharNotInSet(str, NET_MAX_ADDRESS, set);