diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 02454ee4da..45d2ac3662 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -160,6 +160,15 @@
 # define __attribute_pure__ /* Ignore */
 #endif
 
+/* At some point during the gcc 3.1 development the `used' attribute
+   for functions was introduced.  We don't want to use it unconditionally
+   (although this would be possible) since it generates warnings.  */
+#if __GNUC_PREREQ (3,1)
+# define __attribute_used__ __attribute__ ((__used__))
+#else
+# define __attribute_used__ __attribute__ ((__unused__))
+#endif
+
 /* At some point during the gcc 2.8 development the `format_arg' attribute
    for functions was introduced.  We don't want to use it unconditionally
    (although this would be possible) since it generates warnings.