diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -914,4 +914,10 @@
 #define __align_down(x, y) __builtin_align_down(x, y)
 #define __is_aligned(x, y) __builtin_is_aligned(x, y)
 
+#if defined(INVARIANTS) || defined(WITNESS)
+#define        __diagused
+#else
+#define        __diagused      __unused
+#endif
+
 #endif /* !_SYS_CDEFS_H_ */