diff --git a/lib/mining/miner.js b/lib/mining/miner.js
index 8d1fb8f8..20e74406 100644
--- a/lib/mining/miner.js
+++ b/lib/mining/miner.js
@@ -45,6 +45,8 @@ function Miner(options) {
   this.mempool = this.options.mempool;
   this.addresses = this.options.addresses;
 
+  this.locker = this.chain.locker;
+
   this.running = false;
   this.stopping = false;
   this.attempt = null;
@@ -239,6 +241,21 @@ Miner.prototype._onStop = function _onStop() {
  */
 
 Miner.prototype.createBlock = co(function* createBlock(tip, address) {
+  var unlock = yield this.locker.lock();
+  try {
+    return yield this._createBlock(tip, address);
+  } finally {
+    unlock();
+  }
+});
+
+/**
+ * Create a block "attempt" (without a lock).
+ * @param {ChainEntry} tip
+ * @returns {Promise} - Returns {@link MinerBlock}.
+ */
+
+Miner.prototype._createBlock = co(function* createBlock(tip, address) {
   var version = this.options.version;
   var ts, locktime, target, attempt;