diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index 81acb6b243b9..4c4c2af719a8 100644
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -210,7 +210,9 @@
 #define	__packed
 #define	__aligned(x)
 #define	__section(x)
+#define	__weak
 #else
+#define	__weak		__attribute__((__weak__))
 #if !__GNUC_PREREQ__(2, 5) && !defined(__INTEL_COMPILER)
 #define	__dead2
 #define	__pure2