diff --git a/lib/_stream_readable.js b/lib/_stream_readable.js
index 3b614a7924f893..ecdcccc0640ff9 100644
--- a/lib/_stream_readable.js
+++ b/lib/_stream_readable.js
@@ -40,7 +40,9 @@ const {
 } = require('internal/errors').codes;
 const ReadableAsyncIterator = require('internal/streams/async_iterator');
 const { emitExperimentalWarning } = require('internal/util');
-var StringDecoder;
+
+// Lazy loaded to improve the startup performance.
+let StringDecoder;
 
 util.inherits(Readable, Stream);
 
diff --git a/lib/internal/child_process.js b/lib/internal/child_process.js
index a630cff717bcad..1ec3f208660910 100644
--- a/lib/internal/child_process.js
+++ b/lib/internal/child_process.js
@@ -14,7 +14,6 @@ const {
     ERR_MISSING_ARGS
   }
 } = require('internal/errors');
-const { StringDecoder } = require('string_decoder');
 const EventEmitter = require('events');
 const net = require('net');
 const dgram = require('dgram');
@@ -47,6 +46,9 @@ const {
 
 const { SocketListSend, SocketListReceive } = SocketList;
 
+// Lazy loaded for startup performance.
+let StringDecoder;
+
 const MAX_HANDLE_RETRANSMISSIONS = 3;
 
 // this object contain function to convert TCP objects to native handle objects
@@ -476,6 +478,8 @@ function setupChannel(target, channel) {
 
   const control = new Control(channel);
 
+  if (StringDecoder === undefined)
+    StringDecoder = require('string_decoder').StringDecoder;
   var decoder = new StringDecoder('utf8');
   var jsonBuffer = '';
   var pendingHandle = null;
diff --git a/lib/internal/crypto/cipher.js b/lib/internal/crypto/cipher.js
index abf007de5cd623..4a523473804643 100644
--- a/lib/internal/crypto/cipher.js
+++ b/lib/internal/crypto/cipher.js
@@ -28,11 +28,13 @@ const {
 
 const assert = require('assert');
 const LazyTransform = require('internal/streams/lazy_transform');
-const { StringDecoder } = require('string_decoder');
 
 const { inherits } = require('util');
 const { deprecate, normalizeEncoding } = require('internal/util');
 
+// Lazy loaded for startup performance.
+let StringDecoder;
+
 function rsaFunctionFor(method, defaultPadding) {
   return function(options, buffer) {
     const key = options.key || options;
@@ -49,6 +51,8 @@ const privateDecrypt = rsaFunctionFor(_privateDecrypt, RSA_PKCS1_OAEP_PADDING);
 
 function getDecoder(decoder, encoding) {
   encoding = normalizeEncoding(encoding);
+  if (StringDecoder === undefined)
+    StringDecoder = require('string_decoder').StringDecoder;
   decoder = decoder || new StringDecoder(encoding);
   assert(decoder.encoding === encoding, 'Cannot change encoding');
   return decoder;
diff --git a/lib/readline.js b/lib/readline.js
index 124fc8111b2f09..89dd1b84f2dde0 100644
--- a/lib/readline.js
+++ b/lib/readline.js
@@ -35,7 +35,6 @@ const {
 const { debug, inherits } = require('util');
 const { Buffer } = require('buffer');
 const EventEmitter = require('events');
-const { StringDecoder } = require('string_decoder');
 const {
   CSI,
   emitKeys,
@@ -52,6 +51,9 @@ const {
   kClearScreenDown
 } = CSI;
 
+// Lazy load StringDecoder for startup performance.
+let StringDecoder;
+
 const kHistorySize = 30;
 const kMincrlfDelay = 100;
 // \r\n, \n, or \r followed by something other than \n
@@ -73,6 +75,9 @@ function Interface(input, output, completer, terminal) {
     return new Interface(input, output, completer, terminal);
   }
 
+  if (StringDecoder === undefined)
+    StringDecoder = require('string_decoder').StringDecoder;
+
   this._sawReturnAt = 0;
   this.isCompletionEnabled = true;
   this._sawKeyPress = false;
@@ -987,6 +992,9 @@ Interface.prototype._ttyWrite = function(s, key) {
 
 function emitKeypressEvents(stream, iface) {
   if (stream[KEYPRESS_DECODER]) return;
+
+  if (StringDecoder === undefined)
+    StringDecoder = require('string_decoder').StringDecoder;
   stream[KEYPRESS_DECODER] = new StringDecoder('utf8');
 
   stream[ESCAPE_DECODER] = emitKeys(stream);