diff --git a/lib/bcoin/bip151.js b/lib/bcoin/bip151.js
index f462b084..7646fe46 100644
--- a/lib/bcoin/bip151.js
+++ b/lib/bcoin/bip151.js
@@ -95,6 +95,7 @@ utils.inherits(BIP151Stream, EventEmitter);
 
 BIP151Stream.prototype.init = function init(publicKey) {
   var p = bcoin.writer();
+  var iv;
 
   this.publicKey = publicKey;
   this.secret = bcoin.ec.ecdh(this.publicKey, this.privateKey);
@@ -110,8 +111,10 @@ BIP151Stream.prototype.init = function init(publicKey) {
   this.seqHi = 0;
   this.seqLo = 0;
 
-  this.chacha.init(this.k1, this.iv());
-  this.aead.init(this.k2, this.iv());
+  iv = this.iv();
+
+  this.chacha.init(this.k1, iv);
+  this.aead.init(this.k2, iv);
 
   this.lastRekey = utils.now();
 };
@@ -142,6 +145,8 @@ BIP151Stream.prototype.maybeRekey = function maybeRekey(data) {
  */
 
 BIP151Stream.prototype.rekey = function rekey() {
+  var iv;
+
   assert(this.prk, 'Cannot rekey before initialization.');
 
   // All state is reinitialized
@@ -149,8 +154,10 @@ BIP151Stream.prototype.rekey = function rekey() {
   this.k1 = utils.hash256(this.k1);
   this.k2 = utils.hash256(this.k2);
 
-  this.chacha.init(this.k1, this.iv());
-  this.aead.init(this.k2, this.iv());
+  iv = this.iv();
+
+  this.chacha.init(this.k1, iv);
+  this.aead.init(this.k2, iv);
 };
 
 /**
@@ -161,6 +168,8 @@ BIP151Stream.prototype.rekey = function rekey() {
  */
 
 BIP151Stream.prototype.sequence = function sequence() {
+  var iv;
+
   // Wrap sequence number a la openssh.
   if (++this.seqLo === 0x100000000) {
     this.seqLo = 0;
@@ -168,10 +177,12 @@ BIP151Stream.prototype.sequence = function sequence() {
       this.seqHi = 0;
   }
 
+  iv = this.iv();
+
   // State of the ciphers is
   // unaltered aside from the iv.
-  this.chacha.init(null, this.iv());
-  this.aead.init(null, this.iv());
+  this.chacha.init(null, iv);
+  this.aead.init(null, iv);
 };
 
 /**
@@ -179,12 +190,12 @@ BIP151Stream.prototype.sequence = function sequence() {
  * @returns {Buffer}
  */
 
-BIP151Stream.prototype.iv = function iv() {
-  var p = bcoin.writer();
-  p.writeU32(this.seqLo);
-  p.writeU32(this.seqHi);
-  p.writeU32(0);
-  return p.render();
+BIP151Stream.prototype.iv = function _iv() {
+  var iv = new Buffer(12);
+  iv.writeUInt32LE(this.seqLo, 0, true);
+  iv.writeUInt32LE(this.seqHi, 4, true);
+  iv.writeUInt32LE(0, 8, true);
+  return iv;
 };
 
 /**
@@ -289,7 +300,7 @@ BIP151Stream.prototype.feed = function feed(data) {
       if (this.pendingHeaderTotal < 4)
         break;
 
-      chunk = Buffer.concat(this.pendingHeader);
+      chunk = concat(this.pendingHeader);
 
       this.pendingHeaderTotal = 0;
       this.pendingHeader.length = 0;
@@ -321,7 +332,7 @@ BIP151Stream.prototype.feed = function feed(data) {
     if (this.pendingTotal < this.waiting)
       break;
 
-    chunk = Buffer.concat(this.pending);
+    chunk = concat(this.pending);
     payload = chunk.slice(0, this.waiting - 16);
     tag = chunk.slice(this.waiting - 16, this.waiting);
     data = chunk.slice(this.waiting);
@@ -637,6 +648,16 @@ BIP151.prototype.packet = function packet(cmd, body) {
   return this.output.packet(cmd, body);
 };
 
+/*
+ * Helpers
+ */
+
+function concat(buffers) {
+  return buffers.length > 1
+    ? Buffer.concat(buffers)
+    : buffers[0];
+}
+
 /*
  * Expose
  */