diff --git a/lib/dns/rdataset.c b/lib/dns/rdataset.c
index 3e2e433129..48a2ea3efa 100644
--- a/lib/dns/rdataset.c
+++ b/lib/dns/rdataset.c
@@ -263,9 +263,6 @@ dns_rdataset_towire(dns_rdataset_t *rdataset,
 {
 	dns_rdata_t rdata;
 	isc_region_t r;
-	dns_rdataclass_t rclass;
-	dns_rdatatype_t rtype;
-	dns_ttl_t rttl;
 	dns_result_t result;
 
 	/*
@@ -290,27 +287,15 @@ dns_rdataset_towire(dns_rdataset_t *rdataset,
 				+ sizeof(dns_ttl_t)
 				+ 2)) /* XXX 2? it's for the rdata length */
 			return (DNS_R_NOSPACE);
-		rtype = rdataset->type;
-		r.base[0] = (rtype & 0xff00) >> 8;
-		r.base[1] = (rtype & 0xff);
-		rclass = rdataset->class;
-		r.base[2] = (rclass & 0xff00) >> 8;
-		r.base[3] = (rclass & 0x00ff);
-		rttl = rdataset->ttl;
-		r.base[4] = (rttl & 0xff000000) >> 24;
-		r.base[5] = (rttl & 0x00ff0000) >> 16;
-		r.base[6] = (rttl & 0x0000ff00) >> 8;
-		r.base[7] = (rttl & 0x000000ff);
-		isc_buffer_add(target, (sizeof(dns_rdataclass_t)
-					+ sizeof(dns_rdatatype_t)
-					+ sizeof(dns_ttl_t)
-					+ 2)); /* XXX see XXX above */
+		isc_buffer_putuint16(target, rdataset->type);
+		isc_buffer_putuint16(target, rdataset->class);
+		isc_buffer_putuint32(target, rdataset->ttl);
+
 		/*
 		 * copy out the rdata length
 		 */
 		dns_rdataset_current(rdataset, &rdata);
-		r.base[8] = (rdata.length & 0xff00) >> 8;
-		r.base[9] = (rdata.length & 0x00ff);
+		isc_buffer_putuint16(target, rdata.length);
 
 		/*
 		 * copy out the rdata
diff --git a/lib/isc/buffer.c b/lib/isc/buffer.c
index 62f16304d4..f8ed735cdc 100644
--- a/lib/isc/buffer.c
+++ b/lib/isc/buffer.c
@@ -294,6 +294,21 @@ isc_buffer_getuint16(isc_buffer_t *b) {
 	return (result);
 }
 
+void
+isc_buffer_putuint16(isc_buffer_t *b, isc_uint16_t val)
+{
+	unsigned char *cp;
+
+	REQUIRE(VALID_BUFFER(b));
+	REQUIRE(b->used + 2 <= b->length);
+
+	cp = b->base;
+	cp += b->used;
+	b->used += 2;
+	cp[0] = (val & 0xff00) >> 8;
+	cp[1] = (val & 0x00ff);
+}
+
 isc_uint32_t
 isc_buffer_getuint32(isc_buffer_t *b) {
 	unsigned char *cp;
@@ -317,3 +332,20 @@ isc_buffer_getuint32(isc_buffer_t *b) {
 
 	return (result);
 }
+
+void
+isc_buffer_putuint32(isc_buffer_t *b, isc_uint32_t val)
+{
+	unsigned char *cp;
+
+	REQUIRE(VALID_BUFFER(b));
+	REQUIRE(b->used + 4 <= b->length);
+
+	cp = b->base;
+	cp += b->used;
+	b->used += 4;
+	cp[0] = (val & 0xff000000) >> 24;
+	cp[1] = (val & 0x00ff0000) >> 16;
+	cp[2] = (val & 0x0000ff00) >> 8;
+	cp[3] = (val & 0x000000ff);
+}
diff --git a/lib/isc/include/isc/buffer.h b/lib/isc/include/isc/buffer.h
index d2e126fd5f..7f6d43974f 100644
--- a/lib/isc/include/isc/buffer.h
+++ b/lib/isc/include/isc/buffer.h
@@ -366,6 +366,21 @@ isc_buffer_getuint16(isc_buffer_t *b);
  *	A 16-bit unsigned integer.
  */
 
+void
+isc_buffer_putuint16(isc_buffer_t *b, isc_uint16_t val);
+/*
+ * Store an unsigned 16-bit integer in host byte order from 'val'
+ * into 'b' in network byte order.
+ *
+ * Requires:
+ *	'b' is a valid buffer.
+ *
+ *	The length of the unused region of 'b' is at least 2.
+ *
+ * Ensures:
+ *	The used pointer in 'b' is advanced by 2.
+ */
+
 isc_uint32_t
 isc_buffer_getuint32(isc_buffer_t *b);
 /*
@@ -387,4 +402,19 @@ isc_buffer_getuint32(isc_buffer_t *b);
  *	A 32-bit unsigned integer.
  */
 
+void
+isc_buffer_putuint32(isc_buffer_t *b, isc_uint32_t val);
+/*
+ * Store an unsigned 32-bit integer in host byte order from 'val'
+ * into 'b' in network byte order.
+ *
+ * Requires:
+ *	'b' is a valid buffer.
+ *
+ *	The length of the unused region of 'b' is at least 4.
+ *
+ * Ensures:
+ *	The used pointer in 'b' is advanced by 4.
+ */
+
 #endif /* ISC_BUFFER_H */