diff --git a/lib/DefinePlugin.js b/lib/DefinePlugin.js
index cb1835d77..a99cb9a76 100644
--- a/lib/DefinePlugin.js
+++ b/lib/DefinePlugin.js
@@ -11,6 +11,7 @@ const NullFactory = require("./NullFactory");
 
 /** @typedef {import("./Compiler")} Compiler */
 /** @typedef {import("./Parser")} Parser */
+/** @typedef {null|undefined|RegExp|Function|Object} CodeValue */
 
 class RuntimeValue {
 	constructor(fn, fileDependencies) {
@@ -42,7 +43,7 @@ const stringifyObj = (obj, parser) => {
 
 /**
  * Convert code to a string that evaluates
- * @param {null|undefined|RegExp|Function|Object} code Code to evaluate
+ * @param {CodeValue} code Code to evaluate
  * @param {Parser} parser Parser
  * @returns {string} code converted to string that evaluates
  */
@@ -99,13 +100,13 @@ class DefinePlugin {
 
 				/**
 				 * Handler
-				 * @param {TODO} parser Parser
+				 * @param {Parser} parser Parser
 				 * @returns {void}
 				 */
 				const handler = parser => {
 					/**
 					 * Walk definitions
-					 * @param {TODO} definitions Definitions map
+					 * @param {Object} definitions Definitions map
 					 * @param {string} prefix Prefix string
 					 * @returns {void}
 					 */
@@ -146,7 +147,7 @@ class DefinePlugin {
 					/**
 					 * Apply Code
 					 * @param {string} key Key
-					 * @param {TODO} code Code
+					 * @param {CodeValue} code Code
 					 * @returns {void}
 					 */
 					const applyDefine = (key, code) => {
diff --git a/package.json b/package.json
index 44ac63915..4c8987374 100644
--- a/package.json
+++ b/package.json
@@ -73,7 +73,7 @@
     "script-loader": "~0.7.0",
     "simple-git": "^1.65.0",
     "style-loader": "^0.19.1",
-    "typescript": "^2.9.1",
+    "typescript": "^3.0.0-dev.20180622",
     "url-loader": "^0.6.2",
     "val-loader": "^1.0.2",
     "vm-browserify": "~0.0.0",
diff --git a/yarn.lock b/yarn.lock
index 037df12f4..564a6a30d 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -6502,9 +6502,9 @@ typedarray@^0.0.6:
   version "0.0.6"
   resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
 
-typescript@^2.9.1:
-  version "2.9.2"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.9.2.tgz#1cbf61d05d6b96269244eb6a3bce4bd914e0f00c"
+typescript@^3.0.0-dev.20180622:
+  version "3.0.0-dev.20180622"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.0.0-dev.20180622.tgz#16cb2d9cd90cda892810439f75b0b92762b8e745"
 
 ua-parser-js@^0.7.9:
   version "0.7.18"