diff --git a/xen/include/asm-x86/bitops.h b/xen/include/asm-x86/bitops.h
index 4c954663eb..a1e0754b82 100644
--- a/xen/include/asm-x86/bitops.h
+++ b/xen/include/asm-x86/bitops.h
@@ -246,7 +246,7 @@ static __inline__ int constant_test_bit(int nr, const volatile void * addr)
 	return ((1U << (nr & 31)) & (((const volatile unsigned int *) addr)[nr >> 5])) != 0;
 }
 
-static __inline__ int variable_test_bit(int nr, volatile void * addr)
+static __inline__ int variable_test_bit(int nr, const volatile void * addr)
 {
 	int oldbit;