diff --git a/lib/dns/dst_api.c b/lib/dns/dst_api.c
index 5eb43fec80..16629c53c2 100644
--- a/lib/dns/dst_api.c
+++ b/lib/dns/dst_api.c
@@ -31,7 +31,7 @@
 
 /*
  * Principal Author: Brian Wellington
- * $Id: dst_api.c,v 1.38 2009/10/12 06:05:29 marka Exp $
+ * $Id: dst_api.c,v 1.39 2009/10/12 08:57:38 marka Exp $
  */
 
 /*! \file */
@@ -931,7 +931,7 @@ pub_compare(const dst_key_t *key1, const dst_key_t *key2) {
 	/* Zero out flags. */
 	buf1[0] = buf1[1] = 0;
 	if ((key1->key_flags & DNS_KEYFLAG_EXTENDED) != 0)
-		isc_buffer_subtract(&b1, 2);
+		buf1[4] = buf1[5] = 0;
 
 	isc_buffer_init(&b2, buf2, sizeof(buf2));
 	result = dst_key_todns(key2, &b2);
@@ -940,7 +940,7 @@ pub_compare(const dst_key_t *key1, const dst_key_t *key2) {
 	/* Zero out flags. */
 	buf2[0] = buf2[1] = 0;
 	if ((key2->key_flags & DNS_KEYFLAG_EXTENDED) != 0)
-		isc_buffer_subtract(&b2, 2);
+		buf2[4] = buf2[5] = 0;
 
 	isc_buffer_usedregion(&b1, &r1);
 	isc_buffer_usedregion(&b2, &r2);