diff --git a/lib/dns/include/dns/nsec3.h b/lib/dns/include/dns/nsec3.h
index 588dd053c0..c7bf853b56 100644
--- a/lib/dns/include/dns/nsec3.h
+++ b/lib/dns/include/dns/nsec3.h
@@ -43,7 +43,7 @@
 /*
  * Test "unknown" algorithm.  Is mapped to dns_hash_sha1.
  */
-#define DNS_NSEC3_UNKNOWNALG 245U
+#define DNS_NSEC3_UNKNOWNALG ((dns_hash_t)245U)
 
 ISC_LANG_BEGINDECLS