diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 05cfed4..975207c 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -106,5 +106,6 @@
 extern void early_iounmap(void __iomem *addr, unsigned long size);
 extern void __iomem *fix_ioremap(unsigned idx, unsigned long phys);
 
+#define IO_SPACE_LIMIT 0xffff
 
 #endif /* _ASM_X86_IO_H */