diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -394,6 +394,13 @@
 #define	__printf0like(fmtarg, firstvararg)
 #endif
 
+/* To silence warnings about null terminator not fitting into an array. */
+#if __has_attribute(__nonstring__)
+#define	__nonstring	__attribute__((__nonstring__))
+#else
+#define	__nonstring
+#endif
+
 #define	__strong_reference(sym,aliassym)	\
 	extern __typeof (sym) aliassym __attribute__ ((__alias__ (#sym)))
 #ifdef __STDC__
diff --git a/tools/build/cross-build/include/common/sys/cdefs.h b/tools/build/cross-build/include/common/sys/cdefs.h
--- a/tools/build/cross-build/include/common/sys/cdefs.h
+++ b/tools/build/cross-build/include/common/sys/cdefs.h
@@ -100,6 +100,14 @@
 	__attribute__((__format__(__printf0__, fmtarg, firstvararg)))
 #endif
 
+#ifndef __nonstring
+#if __has_attribute(__nonstring__)
+#define	__nonstring	__attribute__((__nonstring__))
+#else
+#define	__nonstring
+#endif
+#endif
+
 #ifndef __predict_true
 #define __predict_true(exp) __builtin_expect((exp), 1)
 #endif