diff --git a/include/asm-arm/io.h b/include/asm-arm/io.h
index cfa71a0..5c4ae8f 100644
--- a/include/asm-arm/io.h
+++ b/include/asm-arm/io.h
@@ -136,9 +136,9 @@
 /*
  * String version of IO memory access ops:
  */
-extern void _memcpy_fromio(void *, void __iomem *, size_t);
-extern void _memcpy_toio(void __iomem *, const void *, size_t);
-extern void _memset_io(void __iomem *, int, size_t);
+extern void _memcpy_fromio(void *, const volatile void __iomem *, size_t);
+extern void _memcpy_toio(volatile void __iomem *, const void *, size_t);
+extern void _memset_io(volatile void __iomem *, int, size_t);
 
 #define mmiowb()