diff --git a/include/asm-m32r/system.h b/include/asm-m32r/system.h
index 9e618af..4ce0619 100644
--- a/include/asm-m32r/system.h
+++ b/include/asm-m32r/system.h
@@ -328,15 +328,15 @@
 #define smp_rmb()	rmb()
 #define smp_wmb()	wmb()
 #define smp_read_barrier_depends()	read_barrier_depends()
+#define set_mb(var, value) do { (void) xchg(&var, value); } while (0)
 #else
 #define smp_mb()	barrier()
 #define smp_rmb()	barrier()
 #define smp_wmb()	barrier()
 #define smp_read_barrier_depends()	do { } while (0)
+#define set_mb(var, value) do { var = value; barrier(); } while (0)
 #endif
 
-#define set_mb(var, value) do { xchg(&var, value); } while (0)
-
 #define arch_align_stack(x) (x)
 
 #endif  /* _ASM_M32R_SYSTEM_H */