--- antlr3config.h.in.orig
+++ antlr3config.h.in
@@ -4,7 +4,9 @@
 #undef ANTLR3_NODEBUGGER
 
 /* Define if 64 bit mode required */
-#undef ANTLR3_USE_64BIT
+#ifdef _LP64
+#define ANTLR3_USE_64BIT
+#endif
 
 /* Define to 1 if you have the `accept' function. */
 #undef HAVE_ACCEPT
