diff --git a/lib/net/packets.js b/lib/net/packets.js
index ac2c0447..c760a18e 100644
--- a/lib/net/packets.js
+++ b/lib/net/packets.js
@@ -1138,6 +1138,8 @@ HeadersPacket.prototype.getSize = function getSize() {
 HeadersPacket.prototype.toWriter = function toWriter(bw) {
   var i, item;
 
+  assert(this.items.length <= 2000, 'Too many headers.');
+
   bw.writeVarint(this.items.length);
 
   for (i = 0; i < this.items.length; i++) {
@@ -1168,6 +1170,8 @@ HeadersPacket.prototype.fromReader = function fromReader(br) {
   var count = br.readVarint();
   var i;
 
+  assert(count <= 2000, 'Too many headers.');
+
   for (i = 0; i < count; i++)
     this.items.push(Headers.fromReader(br));
 
diff --git a/lib/net/peer.js b/lib/net/peer.js
index 9ba17936..9da62fca 100644
--- a/lib/net/peer.js
+++ b/lib/net/peer.js
@@ -2186,7 +2186,7 @@ Peer.prototype.reject = function reject(msg, code, reason, score) {
  */
 
 Peer.prototype.sync = co(function* sync() {
-  var locator, tip, checkpoint;
+  var locator, tip, watermark;
 
   if (!this.pool.syncing)
     return false;
@@ -2220,8 +2220,8 @@ Peer.prototype.sync = co(function* sync() {
 
   if (this.pool.headersFirst) {
     tip = this.chain.tip;
-    checkpoint = this.pool.nextCheckpoint;
-    this.sendGetHeaders([tip.hash], checkpoint.hash);
+    watermark = this.pool.headerTip;
+    this.sendGetHeaders([tip.hash], watermark.hash);
     return true;
   }
 
diff --git a/lib/net/pool.js b/lib/net/pool.js
index 7483e36a..05f4f225 100644
--- a/lib/net/pool.js
+++ b/lib/net/pool.js
@@ -116,7 +116,7 @@ function Pool(options) {
   this.headersFirst = false;
   this.headerChain = new List();
   this.headerNext = null;
-  this.nextCheckpoint = null;
+  this.headerTip = null;
   this.checkpoints = [];
 
   this.peers = new PeerList();
@@ -241,29 +241,26 @@ Pool.prototype._open = co(function* _open() {
 
 Pool.prototype.resetChain = function resetChain() {
   var tip = this.chain.tip;
-  var checkpoint;
+  var watermark;
 
   if (!this.options.headers)
     return;
 
-  if (!this.chain.options.useCheckpoints)
-    return;
-
   this.headersFirst = false;
-  this.nextCheckpoint = null;
+  this.headerTip = null;
   this.headerChain.reset();
   this.headerNext = null;
 
-  checkpoint = this.getNextCheckpoint(tip.height);
+  watermark = this.getNextTip(tip.height);
 
-  if (checkpoint) {
+  if (watermark) {
     this.headersFirst = true;
-    this.nextCheckpoint = checkpoint;
+    this.headerTip = watermark;
     this.headerChain.push(new BlockNode(tip.hash, tip.height));
     this.logger.info(
-      'Initialized header chain to height %d (checkpoint=%d).',
+      'Initialized header chain to height %d (watermark=%d).',
       tip.height,
-      checkpoint.height);
+      watermark.height);
   }
 };
 
@@ -383,7 +380,7 @@ Pool.prototype._disconnect = co(function* disconnect() {
   }
 
   this.headersFirst = false;
-  this.nextCheckpoint = null;
+  this.headerTip = null;
   this.headerChain.reset();
   this.headerNext = null;
 
@@ -594,7 +591,7 @@ Pool.prototype.sendGetAddr = function sendGetAddr() {
  * @returns {Promise}
  */
 
-Pool.prototype.resolveHeaders = co(function* resolveHeaders(peer) {
+Pool.prototype.requestHeaders = co(function* requestHeaders(peer) {
   var items = [];
   var node;
 
@@ -619,15 +616,21 @@ Pool.prototype.resolveHeaders = co(function* resolveHeaders(peer) {
 });
 
 /**
- * Find the next highest checkpoint.
+ * Find the next highest watermark block.
  * @private
  * @param {Number} height
  * @returns {Object}
  */
 
-Pool.prototype.getNextCheckpoint = function getNextCheckpoint(height) {
+Pool.prototype.getNextTip = function getNextTip(height) {
   var i, next;
 
+  if (!this.options.useCheckpoints) {
+    if (this.chain.isFull())
+      return;
+    return new BlockNode(null, height + 20000);
+  }
+
   for (i = 0; i < this.checkpoints.length; i++) {
     next = this.checkpoints[i];
     if (next.height > height)
@@ -1527,7 +1530,7 @@ Pool.prototype.handleHeaders = co(function* handleHeaders(peer, packet) {
 
 Pool.prototype._handleHeaders = co(function* handleHeaders(peer, packet) {
   var headers = packet.items;
-  var isCheckpoint = false;
+  var isWatermark = false;
   var i, header, hash, height, last, node;
 
   if (!this.headersFirst)
@@ -1539,13 +1542,22 @@ Pool.prototype._handleHeaders = co(function* handleHeaders(peer, packet) {
   if (!peer.isLoader())
     return;
 
+  if (headers.length === 0)
+    return;
+
   if (headers.length > 2000) {
-    this.increaseBan(100);
+    peer.increaseBan(100);
     return;
   }
 
-  if (headers.length === 0)
+  if (this.headerChain.size > 40000) {
+    this.logger.warning(
+      'Peer is sending too many headers (%s).',
+      peer.hostname);
+    peer.increaseBan(100);
+    peer.destroy();
     return;
+  }
 
   assert(this.headerChain.size > 0);
 
@@ -1556,13 +1568,16 @@ Pool.prototype._handleHeaders = co(function* handleHeaders(peer, packet) {
     height = last.height + 1;
 
     if (header.prevBlock !== last.hash) {
-      peer.increaseBan(100);
-      throw new Error('Bad header chain.');
+      this.logger.warning('Peer sent a bad header chain (%s).', peer.hostname);
+      peer.destroy();
+      return;
     }
 
     if (!header.verify()) {
+      this.logger.warning('Peer sent an invalid header (%s).', peer.hostname);
       peer.increaseBan(100);
-      throw new Error('Invalid header.');
+      peer.destroy();
+      return;
     }
 
     node = new BlockNode(hash, last.height + 1);
@@ -1570,12 +1585,18 @@ Pool.prototype._handleHeaders = co(function* handleHeaders(peer, packet) {
     if (!this.headerNext)
       this.headerNext = node;
 
-    if (node.height === this.nextCheckpoint.height) {
-      if (node.hash !== this.nextCheckpoint.hash) {
-        peer.increaseBan(100);
-        throw new Error('Bad checkpoint header.');
+    if (node.height === this.headerTip.height) {
+      if (this.options.useCheckpoints) {
+        if (node.hash !== this.headerTip.hash) {
+          this.logger.warning(
+            'Peer sent an invalid checkpoint (%s).',
+            peer.hostname);
+          peer.increaseBan(100);
+          peer.destroy();
+          return;
+        }
       }
-      isCheckpoint = true;
+      isWatermark = true;
     }
 
     this.headerChain.push(node);
@@ -1589,14 +1610,14 @@ Pool.prototype._handleHeaders = co(function* handleHeaders(peer, packet) {
   this.emit('headers', packet, peer);
 
   // Request the hashes we just added.
-  if (isCheckpoint) {
+  if (isWatermark) {
     this.headerChain.shift();
-    yield this.resolveHeaders(peer);
+    yield this.requestHeaders(peer);
     return;
   }
 
   // Restart the getheaders process.
-  peer.sendGetHeaders([node.hash], this.nextCheckpoint.hash);
+  peer.sendGetHeaders([node.hash], this.headerTip.hash);
 });
 
 /**
@@ -1658,8 +1679,8 @@ Pool.prototype.addBlock = co(function* addBlock(peer, block) {
 
 Pool.prototype._addBlock = co(function* addBlock(peer, block) {
   var hash = block.hash('hex');
-  var isCheckpoint = false;
-  var node, checkpoint;
+  var isWatermark = false;
+  var node, watermark;
 
   if (!this.syncing)
     return;
@@ -1677,11 +1698,11 @@ Pool.prototype._addBlock = co(function* addBlock(peer, block) {
     assert(node);
 
     if (hash === node.hash) {
-      if (hash === this.nextCheckpoint.hash) {
+      if (node.height === this.headerTip.height) {
         this.logger.info(
           'Received checkpoint block %s (%d).',
           hash, node.height);
-        isCheckpoint = true;
+        isWatermark = true;
       } else {
         this.headerChain.shift();
       }
@@ -1716,26 +1737,26 @@ Pool.prototype._addBlock = co(function* addBlock(peer, block) {
   if (!this.headersFirst)
     return;
 
-  if (!isCheckpoint) {
-    yield this.resolveHeaders(peer);
+  if (!isWatermark && !this.chain.isFull()) {
+    yield this.requestHeaders(peer);
     return;
   }
 
-  node = this.nextCheckpoint;
-  checkpoint = this.getNextCheckpoint(node.height);
+  node = this.headerTip;
+  watermark = this.getNextTip(node.height);
 
-  if (checkpoint) {
-    this.nextCheckpoint = checkpoint;
-    peer.sendGetHeaders([node.hash], checkpoint.hash);
+  if (watermark) {
+    this.headerTip = watermark;
+    peer.sendGetHeaders([hash], watermark.hash);
     return;
   }
 
   this.headersFirst = false;
-  this.nextCheckpoint = null;
+  this.headerTip = null;
   this.headerChain.reset();
   this.headerNext = null;
 
-  peer.sendGetBlocks([hash], null);
+  yield this.getBlocks(peer, hash);
 });
 
 /**
@@ -2884,6 +2905,7 @@ function PoolOptions(options) {
   this.mempool = null;
 
   this.witness = this.network.witness;
+  this.useCheckpoints = false;
   this.spv = false;
   this.listen = false;
   this.headers = false;
@@ -2956,6 +2978,14 @@ PoolOptions.prototype.fromOptions = function fromOptions(options) {
     this.witness = this.chain.options.witness;
   }
 
+  if (options.useCheckpoints != null) {
+    assert(typeof options.useCheckpoints === 'boolean');
+    assert(options.useCheckpoints === this.chain.options.useCheckpoints);
+    this.useCheckpoints = options.useCheckpoints;
+  } else {
+    this.useCheckpoints = this.chain.options.useCheckpoints;
+  }
+
   if (options.spv != null) {
     assert(typeof options.spv === 'boolean');
     assert(options.spv === this.chain.options.spv);