diff --git a/include/asm-i386/system.h b/include/asm-i386/system.h
index 36a92ed6a9d0..399145a247f2 100644
--- a/include/asm-i386/system.h
+++ b/include/asm-i386/system.h
@@ -507,7 +507,7 @@ struct alt_instr {
 #define smp_rmb()	rmb()
 #define smp_wmb()	wmb()
 #define smp_read_barrier_depends()	read_barrier_depends()
-#define set_mb(var, value) do { xchg(&var, value); } while (0)
+#define set_mb(var, value) do { (void) xchg(&var, value); } while (0)
 #else
 #define smp_mb()	barrier()
 #define smp_rmb()	barrier()
diff --git a/include/asm-x86_64/system.h b/include/asm-x86_64/system.h
index a73f0c789d8b..b7f66034ae7a 100644
--- a/include/asm-x86_64/system.h
+++ b/include/asm-x86_64/system.h
@@ -327,7 +327,7 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 #define wmb()	asm volatile("" ::: "memory")
 #endif
 #define read_barrier_depends()	do {} while(0)
-#define set_mb(var, value) do { xchg(&var, value); } while (0)
+#define set_mb(var, value) do { (void) xchg(&var, value); } while (0)
 #define set_wmb(var, value) do { var = value; wmb(); } while (0)
 
 #define warn_if_not_ulong(x) do { unsigned long foo; (void) (&(x) == &foo); } while (0)