diff --git a/lib/bcoin/chain.js b/lib/bcoin/chain.js
index ba60c3f2..9025f4e9 100644
--- a/lib/bcoin/chain.js
+++ b/lib/bcoin/chain.js
@@ -42,6 +42,7 @@ function Chain(node, options) {
   this.lastUpdate = utils.now();
   this.tip = null;
   this.height = -1;
+  this.segwitActive = null;
 
   this.orphan = {
     map: {},
@@ -153,20 +154,25 @@ Chain.prototype._init = function _init() {
       if (err)
         return self.emit('error', err);
 
-      self.db.getTip(function(err, tip) {
+      self.isSegwitActive(function(err) {
         if (err)
           return self.emit('error', err);
 
-        assert(tip);
+        self.db.getTip(function(err, tip) {
+          if (err)
+            return self.emit('error', err);
 
-        self.tip = tip;
-        self.height = tip.height;
+          assert(tip);
 
-        self.loaded = true;
-        self.emit('open');
+          self.tip = tip;
+          self.height = tip.height;
 
-        if (self.isFull())
-          self.emit('full');
+          self.loaded = true;
+          self.emit('open');
+
+          if (self.isFull())
+            self.emit('full');
+        });
       });
     });
   });
@@ -489,6 +495,9 @@ Chain.prototype._verify = function _verify(block, prev, peer, callback) {
       if (block.version >= 5 && prev.isUpgraded(5)) {
         flags |= constants.flags.VERIFY_WITNESS;
         segwit = true;
+        self.segwitActive = true;
+      } else if (block.version >= 5) {
+        self.segwitActive = false;
       }
     }
 
@@ -1878,6 +1887,41 @@ Chain.prototype.computeBlockVersion = function computeBlockVersion(prev, callbac
   });
 };
 
+Chain.prototype.isSegwitActive = function isSegwitActive(callback) {
+  var tip = this.tip;
+  var unlock;
+
+  if (this.segwitActive != null)
+    return utils.asyncify(callback)(null, this.segwitActive);
+
+  if (!tip)
+    return utils.asyncify(callback)(null, false);
+
+  if (!(network.segwitHeight !== -1 && height >= network.segwitHeight))
+    return utils.asyncify(callback)(null, false);
+
+  unlock = this._lock(isSegwitActive, [callback]);
+  if (!unlock)
+    return;
+
+  callback = utils.wrap(callback, unlock);
+
+  tip.ensureAncestors(function(err) {
+    if (err)
+      return callback(err);
+
+    if (!tip.isUpgraded(5)) {
+      tip.free();
+      self.segwitActive = false;
+      return callback(null, false);
+    }
+
+    tip.free();
+    self.segwitActive = true;
+    return callback(null, true);
+  });
+};
+
 /**
  * Expose
  */
diff --git a/lib/bcoin/mempool.js b/lib/bcoin/mempool.js
index 757a51c0..88403141 100644
--- a/lib/bcoin/mempool.js
+++ b/lib/bcoin/mempool.js
@@ -339,8 +339,8 @@ Mempool.prototype.addTX = function addTX(tx, peer, callback, force) {
 
         if (!tx.hasPrevout()) {
           if (self.size > Mempool.MAX_MEMPOOL_SIZE) {
-            return callback(
-              new VerifyError('insufficientfee',
+            return callback(new VerifyError(
+              'insufficientfee',
               'mempool full',
               0));
           }
@@ -359,8 +359,8 @@ Mempool.prototype.addTX = function addTX(tx, peer, callback, force) {
               return callback(err);
 
             if (!result) {
-              return callback(
-                new VerifyError('insufficientfee',
+              return callback(new VerifyError(
+                'insufficientfee',
                 'mempool full',
                 0));
             }
@@ -415,13 +415,18 @@ Mempool.prototype.verify = function verify(tx, callback) {
   var self = this;
   var height = this.chain.height + 1;
   var total, input, coin, i, fee, now, free, minFee;
+  var flags = Mempool.flags;
+  var mandatory = Mempool.mandatory;
 
-  if (network.type !== 'segwit') {
+  if (this.chain.segwitActive) {
+    flags |= constants.flags.VERIFY_WITNESS;
+    mandatory |= constants.flags.VERIFY_WITNESS;
+  } else {
     if (tx.hasWitness())
       return callback(new VerifyError('nonstandard', 'no-witness-yet', 0));
   }
 
-  if (this.requireStandard && !tx.isStandardInputs(Mempool.flags)) {
+  if (this.requireStandard && !tx.isStandardInputs(flags)) {
     return callback(new VerifyError(
       'nonstandard',
       'bad-txns-nonstandard-inputs',
@@ -529,12 +534,12 @@ Mempool.prototype.verify = function verify(tx, callback) {
     }
 
     // Do this in the worker pool.
-    tx.verifyAsync(null, true, Mempool.flags, function(err, result) {
+    tx.verifyAsync(null, true, flags, function(err, result) {
       if (err)
         return callback(err);
 
       if (!result) {
-        return tx.verifyAsync(null, true, Mempool.mandatory, function(err, result) {
+        return tx.verifyAsync(null, true, mandatory, function(err, result) {
           if (err)
             return callback(err);
 
@@ -545,8 +550,8 @@ Mempool.prototype.verify = function verify(tx, callback) {
               0));
           }
 
-          return callback(
-            new VerifyError('nonstandard',
+          return callback(new VerifyError(
+            'nonstandard',
             'non-mandatory-script-verify-flag',
             0));
         });