diff --git a/include/bsd/sys/cdefs.h b/include/bsd/sys/cdefs.h
index d1cc419..98333d1 100644
--- a/include/bsd/sys/cdefs.h
+++ b/include/bsd/sys/cdefs.h
@@ -155,6 +155,12 @@
 # define __bounded__(x, y, z)
 #endif
 
+/*
+ * Return the number of elements in a statically-allocated array,
+ * __x.
+ */
+#define	__arraycount(__x)	(sizeof(__x) / sizeof(__x[0]))
+
 /*
  * We define this here since <stddef.h>, <sys/queue.h>, and <sys/types.h>
  * require it.