diff --git a/lib/chain/chaindb.js b/lib/chain/chaindb.js
index ade11f08..96c1e549 100644
--- a/lib/chain/chaindb.js
+++ b/lib/chain/chaindb.js
@@ -596,27 +596,17 @@ ChainDB.prototype.getNextHash = co(function* getNextHash(hash) {
  */
 
 ChainDB.prototype.isMainChain = co(function* isMainChain(hash) {
-  var query, height, existing;
-
-  if (hash instanceof ChainEntry) {
-    query = hash.height;
-    hash = hash.hash;
-  } else {
-    query = hash;
-  }
+  assert(typeof hash === 'string');
 
   if (hash === this.chain.tip.hash
       || hash === this.network.genesis.hash) {
     return true;
   }
 
-  height = yield this.getHeight(query);
-  existing = yield this.getHash(height);
+  if (yield this.getNextHash(hash))
+    return true;
 
-  if (!existing)
-    return false;
-
-  return hash === existing;
+  return false;
 });
 
 /**
diff --git a/lib/chain/chainentry.js b/lib/chain/chainentry.js
index 2bc4dbe8..edb3e23f 100644
--- a/lib/chain/chainentry.js
+++ b/lib/chain/chainentry.js
@@ -223,9 +223,27 @@ ChainEntry.prototype.getAncestors = co(function* getAncestors(max) {
  * @returns {Promise} - Return Boolean.
  */
 
-ChainEntry.prototype.isMainChain = function isMainChain() {
-  return this.chain.db.isMainChain(this);
-};
+ChainEntry.prototype.isMainChain = co(function* isMainChain() {
+  var entry;
+
+  if (this.hash === this.chain.tip.hash
+      || this.hash === this.network.genesis.hash) {
+    return true;
+  }
+
+  entry = this.chain.db.getCache(this.height);
+
+  if (entry) {
+    if (entry.hash === this.hash)
+      return true;
+    return false;
+  }
+
+  if (yield this.chain.db.getNextHash(this.hash))
+    return true;
+
+  return false;
+});
 
 /**
  * Collect ancestors up to `height`.
@@ -234,7 +252,7 @@ ChainEntry.prototype.isMainChain = function isMainChain() {
  */
 
 ChainEntry.prototype.getAncestorByHeight = co(function* getAncestorByHeight(height) {
-  var main, entry;
+  var entry;
 
   if (height < 0)
     return yield co.wait();
@@ -242,9 +260,7 @@ ChainEntry.prototype.getAncestorByHeight = co(function* getAncestorByHeight(heig
   assert(height >= 0);
   assert(height <= this.height);
 
-  main = yield this.isMainChain();
-
-  if (main)
+  if (yield this.isMainChain())
     return yield this.chain.db.get(height);
 
   entry = yield this.getAncestor(this.height - height);