Index: sys/x86/include/bus.h
===================================================================
--- sys/x86/include/bus.h
+++ sys/x86/include/bus.h
@@ -114,7 +114,6 @@
 
 #define BUS_SPACE_MAXSIZE_24BIT	0xFFFFFF
 #define BUS_SPACE_MAXSIZE_32BIT 0xFFFFFFFF
-#define BUS_SPACE_MAXSIZE	0xFFFFFFFF
 #define BUS_SPACE_MAXADDR_24BIT	0xFFFFFF
 #define BUS_SPACE_MAXADDR_32BIT 0xFFFFFFFF
 #if defined(__amd64__) || defined(PAE)
@@ -123,6 +122,11 @@
 #else
 #define BUS_SPACE_MAXADDR	0xFFFFFFFF
 #endif
+#if defined(__amd64__)
+#define BUS_SPACE_MAXSIZE	0xFFFFFFFFFFFFFFFFULL
+#else
+#define BUS_SPACE_MAXSIZE	0xFFFFFFFF
+#endof
 
 #define BUS_SPACE_INVALID_DATA	(~0)
 #define BUS_SPACE_UNRESTRICTED	(~0)