diff --git a/lib/http/rpc.js b/lib/http/rpc.js
index 3f9d582c..cecf97da 100644
--- a/lib/http/rpc.js
+++ b/lib/http/rpc.js
@@ -1633,7 +1633,7 @@ RPC.prototype.createRawTransaction = async function createRawTransaction(args, h
   let inputs = valid.array(0);
   let sendTo = valid.obj(1);
   let locktime = valid.u32(2);
-  let tx, keys, addrs;
+  let tx, addrs;
 
   if (help || args.length < 2 || args.length > 3) {
     throw new RPCError(errs.MISC_ERROR,
@@ -1673,11 +1673,10 @@ RPC.prototype.createRawTransaction = async function createRawTransaction(args, h
     tx.inputs.push(input);
   }
 
-  keys = Object.keys(sendTo);
   valid = new Validator([sendTo]);
   addrs = {};
 
-  for (let key of keys) {
+  for (let key of Object.keys(sendTo)) {
     let addr, b58, value, output;
 
     if (key === 'data') {
diff --git a/lib/net/bip150.js b/lib/net/bip150.js
index 2cea3c45..7dac2382 100644
--- a/lib/net/bip150.js
+++ b/lib/net/bip150.js
@@ -576,11 +576,9 @@ AuthDB.prototype.addAuthorized = function addAuthorized(key) {
  */
 
 AuthDB.prototype.setKnown = function setKnown(map) {
-  let keys = Object.keys(map);
-
   this.known.clear();
 
-  for (let host of keys) {
+  for (let host of Object.keys(map)) {
     let key = map[host];
     this.addKnown(host, key);
   }
diff --git a/lib/node/config.js b/lib/node/config.js
index af227a22..0f45ae91 100644
--- a/lib/node/config.js
+++ b/lib/node/config.js
@@ -63,9 +63,7 @@ Config.alias = {
  */
 
 Config.prototype.inject = function inject(options) {
-  let keys = Object.keys(options);
-
-  for (let key of keys) {
+  for (let key of Object.keys(options)) {
     let value = options[key];
 
     switch (key) {
@@ -787,7 +785,6 @@ Config.prototype.parseArg = function parseArg(argv) {
 
 Config.prototype.parseEnv = function parseEnv(env) {
   let prefix = this.module;
-  let keys;
 
   prefix = prefix.toUpperCase();
   prefix = prefix.replace(/-/g, '_');
@@ -798,9 +795,7 @@ Config.prototype.parseEnv = function parseEnv(env) {
 
   assert(env && typeof env === 'object');
 
-  keys = Object.keys(env);
-
-  for (let key of keys) {
+  for (let key of Object.keys(env)) {
     let value, alias;
 
     if (key.indexOf(prefix) !== 0)
diff --git a/lib/protocol/network.js b/lib/protocol/network.js
index b6e89783..ca25ca33 100644
--- a/lib/protocol/network.js
+++ b/lib/protocol/network.js
@@ -90,7 +90,6 @@ Network.simnet = null;
 
 Network.prototype._init = function _init() {
   let bits = 0;
-  let keys;
 
   for (let deployment of this.deploys)
     bits |= 1 << deployment.bit;
@@ -99,9 +98,7 @@ Network.prototype._init = function _init() {
 
   this.unknownBits = ~bits;
 
-  keys = Object.keys(this.checkpointMap);
-
-  for (let key of keys) {
+  for (let key of Object.keys(this.checkpointMap)) {
     let hash = this.checkpointMap[key];
     let height = +key;
 
diff --git a/lib/utils/ip.js b/lib/utils/ip.js
index 1969f5e1..f7f9e067 100644
--- a/lib/utils/ip.js
+++ b/lib/utils/ip.js
@@ -981,10 +981,9 @@ IP.isEqual = function isEqual(a, b) {
 
 IP.getInterfaces = function _getInterfaces(name, family) {
   let interfaces = os.networkInterfaces();
-  let keys = Object.keys(interfaces);
   let result = [];
 
-  for (let key of keys) {
+  for (let key of Object.keys(interfaces)) {
     let items = interfaces[key];
 
     for (let details of items) {
diff --git a/lib/utils/util.js b/lib/utils/util.js
index 920acf13..7795f878 100644
--- a/lib/utils/util.js
+++ b/lib/utils/util.js
@@ -664,9 +664,8 @@ util.toMap = function toMap(items) {
 
 util.revMap = function revMap(map) {
   let reversed = {};
-  let keys = Object.keys(map);
 
-  for (let key of keys)
+  for (let key of Object.keys(map))
     reversed[map[key]] = key;
 
   return reversed;
@@ -679,13 +678,12 @@ util.revMap = function revMap(map) {
  */
 
 util.values = function values(map) {
-  let keys = Object.keys(map);
-  let out = [];
+  let items = [];
 
-  for (let key of keys)
-    out.push(map[key]);
+  for (let key of Object.keys(map))
+    items.push(map[key]);
 
-  return out;
+  return items;
 };
 
 /**
diff --git a/lib/wallet/rpc.js b/lib/wallet/rpc.js
index 31ee1a4b..f1a518b3 100644
--- a/lib/wallet/rpc.js
+++ b/lib/wallet/rpc.js
@@ -906,7 +906,7 @@ RPC.prototype._listReceived = async function _listReceived(minconf, empty, watch
   let out = [];
   let result = [];
   let map = {};
-  let txs, keys;
+  let txs;
 
   for (let path of paths) {
     let addr = path.toAddress();
@@ -947,9 +947,7 @@ RPC.prototype._listReceived = async function _listReceived(minconf, empty, watch
     }
   }
 
-  keys = Object.keys(map);
-
-  for (let key of keys) {
+  for (let key of Object.keys(map)) {
     let entry = map[key];
     out.push(entry);
   }
@@ -1323,7 +1321,7 @@ RPC.prototype.sendMany = async function sendMany(args, help) {
   let subtractFee = valid.bool(4, false);
   let outputs = [];
   let uniq = {};
-  let keys, options, tx;
+  let options, tx;
 
   if (help || args.length < 2 || args.length > 5) {
     throw new RPCError(errs.MISC_ERROR,
@@ -1337,10 +1335,9 @@ RPC.prototype.sendMany = async function sendMany(args, help) {
   if (!sendTo)
     throw new RPCError(errs.TYPE_ERROR, 'Invalid parameter.');
 
-  keys = Object.keys(sendTo);
   valid = new Validator([sendTo]);
 
-  for (let key of keys) {
+  for (let key of Object.keys(sendTo)) {
     let value = valid.btc(key);
     let addr = parseAddress(key, this.network);
     let hash = addr.getHash('hex');