diff --git a/lib/primitives/abstractblock.js b/lib/primitives/abstractblock.js
index dade5bef..e0ecfc06 100644
--- a/lib/primitives/abstractblock.js
+++ b/lib/primitives/abstractblock.js
@@ -58,6 +58,7 @@ function AbstractBlock(options) {
 
   this._valid = null;
   this._hash = null;
+  this._hhash = null;
   this._size = null;
   this._witnessSize = null;
 
@@ -140,6 +141,7 @@ AbstractBlock.prototype.parseJSON = function parseJSON(json) {
 
 AbstractBlock.prototype.hash = function hash(enc) {
   var hash = this._hash;
+  var hex;
 
   if (!hash) {
     hash = crypto.hash256(this.abbr());
@@ -147,7 +149,17 @@ AbstractBlock.prototype.hash = function hash(enc) {
       this._hash = hash;
   }
 
-  return enc === 'hex' ? hash.toString('hex') : hash;
+  if (enc === 'hex') {
+    hex = this._hhash;
+    if (!hex) {
+      hex = hash.toString('hex');
+      if (!this.mutable)
+        this._hhash = hex;
+    }
+    hash = hex;
+  }
+
+  return hash;
 };
 
 /**
diff --git a/lib/primitives/tx.js b/lib/primitives/tx.js
index f1e8589b..a7cd7e83 100644
--- a/lib/primitives/tx.js
+++ b/lib/primitives/tx.js
@@ -86,6 +86,7 @@ function TX(options) {
   this.mutable = false;
 
   this._hash = null;
+  this._hhash = null;
   this._whash = null;
 
   this._raw = null;
@@ -219,6 +220,7 @@ TX.prototype.unsetBlock = function unsetBlock() {
 
 TX.prototype.hash = function _hash(enc) {
   var hash = this._hash;
+  var hex;
 
   if (!hash) {
     hash = crypto.hash256(this.toNormal());
@@ -226,7 +228,17 @@ TX.prototype.hash = function _hash(enc) {
       this._hash = hash;
   }
 
-  return enc === 'hex' ? hash.toString('hex') : hash;
+  if (enc === 'hex') {
+    hex = this._hhash;
+    if (!hex) {
+      hex = hash.toString('hex');
+      if (!this.mutable)
+        this._hhash = hex;
+    }
+    hash = hex;
+  }
+
+  return hash;
 };
 
 /**
diff --git a/test/script-test.js b/test/script-test.js
index 3b49dd20..82df00fb 100644
--- a/test/script-test.js
+++ b/test/script-test.js
@@ -348,6 +348,8 @@ describe('Script', function() {
           tx._witnessSize = -1;
           tx._lastWitnessSize = 0;
           tx._hash = null;
+          tx._hhash = null;
+          tx._whash = null;
           tx._inputValue = -1;
           tx._outputValue = -1;
           tx._hashPrevouts = null;
diff --git a/test/tx-test.js b/test/tx-test.js
index 6f2911a1..6cd589c0 100644
--- a/test/tx-test.js
+++ b/test/tx-test.js
@@ -47,6 +47,8 @@ function clearCache(tx, nocache) {
   tx._witnessSize = -1;
   tx._lastWitnessSize = 0;
   tx._hash = null;
+  tx._hhash = null;
+  tx._whash = null;
   tx._inputValue = -1;
   tx._outputValue = -1;
   tx._hashPrevouts = null;