Index: head/sys/x86/include/bus.h
===================================================================
--- head/sys/x86/include/bus.h
+++ head/sys/x86/include/bus.h
@@ -114,7 +114,11 @@
 
 #define BUS_SPACE_MAXSIZE_24BIT	0xFFFFFF
 #define BUS_SPACE_MAXSIZE_32BIT 0xFFFFFFFF
+#if defined(__amd64__)
+#define BUS_SPACE_MAXSIZE	0xFFFFFFFFFFFFFFFFULL
+#else
 #define BUS_SPACE_MAXSIZE	0xFFFFFFFF
+#endif
 #define BUS_SPACE_MAXADDR_24BIT	0xFFFFFF
 #define BUS_SPACE_MAXADDR_32BIT 0xFFFFFFFF
 #if defined(__amd64__) || defined(PAE)