diff --git a/lib/net/peer.js b/lib/net/peer.js
index 582de881..3a99bc11 100644
--- a/lib/net/peer.js
+++ b/lib/net/peer.js
@@ -117,6 +117,7 @@ function Peer(options) {
   this.merkleBlock = null;
   this.merkleTime = -1;
   this.merkleMatches = 0;
+  this.merkleMap = null;
   this.syncing = false;
   this.sentAddr = false;
   this.sentGetAddr = false;
diff --git a/lib/net/pool.js b/lib/net/pool.js
index ea31dcbb..4a02a5aa 100644
--- a/lib/net/pool.js
+++ b/lib/net/pool.js
@@ -736,6 +736,7 @@ Pool.prototype.stopSync = function stopSync() {
     peer.merkleBlock = null;
     peer.merkleTime = -1;
     peer.merkleMatches = 0;
+    peer.merkleMap = null;
     peer.blockTime = -1;
     peer.blockMap.reset();
     peer.compactBlocks.reset();
@@ -2454,18 +2455,34 @@ Pool.prototype._handleTX = co(function* handleTX(peer, packet) {
   var tx = packet.tx;
   var hash = tx.hash('hex');
   var flags = chainCommon.flags.VERIFY_NONE;
+  var block = peer.merkleBlock;
   var missing;
 
-  if (peer.merkleBlock) {
+  if (block) {
     assert(peer.merkleMatches > 0);
-    if (peer.merkleBlock.hasTX(hash)) {
-      peer.merkleBlock.addTX(tx);
-      if (--peer.merkleMatches === 0) {
-        yield this._addBlock(peer, peer.merkleBlock, flags);
-        peer.merkleTime = -1;
-        peer.merkleBlock = null;
-        peer.merkleMatches = 0;
+    assert(peer.merkleMap);
+
+    if (block.hasTX(hash)) {
+      if (peer.merkleMap.has(hash)) {
+        this.logger.warning(
+          'Peer sent duplicate merkle tx: %s (%s).',
+          tx.txid(), peer.hostname());
+        peer.increaseBan(100);
+        return;
       }
+
+      peer.merkleMap.insert(hash);
+
+      block.addTX(tx);
+
+      if (--peer.merkleMatches === 0) {
+        peer.merkleBlock = null;
+        peer.merkleTime = -1;
+        peer.merkleMatches = 0;
+        peer.merkleMap = null;
+        yield this._addBlock(peer, block, flags);
+      }
+
       return;
     }
   }
@@ -2684,9 +2701,10 @@ Pool.prototype._handleMerkleBlock = co(function* handleMerkleBlock(peer, packet)
     return;
   }
 
-  peer.merkleTime = util.ms();
   peer.merkleBlock = block;
+  peer.merkleTime = util.ms();
   peer.merkleMatches = block.tree.matches.length;
+  peer.merkleMap = new Map();
 });
 
 /**