diff --git a/lib/dns/include/dns/rdataset.h b/lib/dns/include/dns/rdataset.h
index 94c89d8e4c..d551767368 100644
--- a/lib/dns/include/dns/rdataset.h
+++ b/lib/dns/include/dns/rdataset.h
@@ -191,7 +191,12 @@ dns_rdataset_totext(dns_rdataset_t *rdataset,
  * Notes:
  *	The rdata cursor position will be changed.
  *
- * XXX Supply Requires and Ensures XXX
+ * Requires:
+ *	'rdataset' is a valid rdataset.
+ *
+ *	'rdataset' is not empty.
+ *
+ * XXX Supply more Requires and Ensures XXX
  */
 
 dns_result_t
@@ -206,6 +211,11 @@ dns_rdataset_towire(dns_rdataset_t *rdataset,
  * Notes:
  *	The rdata cursor position will be changed.
  *
+ * Requires:
+ *	'rdataset' is a valid rdataset.
+ *
+ *	'rdataset' is not empty.
+ *
  * XXX Supply Requires and Ensures XXX
  */