diff --git a/linux-2.6-xen-sparse/include/asm-xen/asm-i386/io.h b/linux-2.6-xen-sparse/include/asm-xen/asm-i386/io.h
index f3e03cd0a9..afb146d561 100644
--- a/linux-2.6-xen-sparse/include/asm-xen/asm-i386/io.h
+++ b/linux-2.6-xen-sparse/include/asm-xen/asm-i386/io.h
@@ -228,7 +228,7 @@ static inline void memcpy_toio(volatile void __iomem *dst, const void *src, int
  * used as the IO-area pointer (it can be iounmapped as well, so the
  * analogy with PCI is quite large):
  */
-#define __ISA_IO_base ((char __iomem *)(PAGE_OFFSET))
+#define __ISA_IO_base ((char __iomem *)(fix_to_virt(FIX_ISAMAP_BEGIN)))
 
 #define isa_readb(a) readb(__ISA_IO_base + (a))
 #define isa_readw(a) readw(__ISA_IO_base + (a))
diff --git a/linux-2.6-xen-sparse/include/asm-xen/asm-x86_64/io.h b/linux-2.6-xen-sparse/include/asm-xen/asm-x86_64/io.h
index 3b729ec0d7..f861c89564 100644
--- a/linux-2.6-xen-sparse/include/asm-xen/asm-x86_64/io.h
+++ b/linux-2.6-xen-sparse/include/asm-xen/asm-x86_64/io.h
@@ -298,7 +298,7 @@ void memset_io(volatile void __iomem *a, int b, size_t c);
  * used as the IO-area pointer (it can be iounmapped as well, so the
  * analogy with PCI is quite large):
  */
-#define __ISA_IO_base ((char __iomem *)(PAGE_OFFSET))
+#define __ISA_IO_base ((char __iomem *)(fix_to_virt(FIX_ISAMAP_BEGIN)))
 
 #define isa_readb(a) readb(__ISA_IO_base + (a))
 #define isa_readw(a) readw(__ISA_IO_base + (a))