diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index e5a2ab44cd5c0de4e93260f99ac0d91d0a75b0c2..4f8e820cf38fa5d2ac904cc2679c59b3470c99a7 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -125,7 +125,7 @@ static inline void *phys_to_virt(phys_addr_t address)
 /*
  * ISA I/O bus memory addresses are 1:1 with the physical address.
  */
-#define isa_virt_to_bus virt_to_phys
+#define isa_virt_to_bus (unsigned long)virt_to_phys
 #define isa_page_to_bus page_to_phys
 #define isa_bus_to_virt phys_to_virt