diff --git a/lib/binaries/chrome_xml.ts b/lib/binaries/chrome_xml.ts
index 5e9cea33..f75ef702 100644
--- a/lib/binaries/chrome_xml.ts
+++ b/lib/binaries/chrome_xml.ts
@@ -61,7 +61,7 @@ export class ChromeXml extends XmlConfigSource {
    */
   private getLatestChromeDriverVersion(): Promise<BinaryUrl> {
     return this.getVersionList().then(list => {
-      let chromedriverVersion = null;
+      let chromedriverVersion: string = null;
       let latest = '';
       let latestVersion = '';
       for (let item of list) {
diff --git a/lib/binaries/iedriver_xml.ts b/lib/binaries/iedriver_xml.ts
index 1ef8e1b0..40ac3ff4 100644
--- a/lib/binaries/iedriver_xml.ts
+++ b/lib/binaries/iedriver_xml.ts
@@ -36,7 +36,7 @@ export class IEDriverXml extends XmlConfigSource {
 
   private getLatestIEDriverVersion(): Promise<BinaryUrl> {
     return this.getVersionList().then(list => {
-      let latestVersion = null;
+      let latestVersion: string = null;
       let latest = '';
       for (let item of list) {
         // Get a semantic version.
diff --git a/lib/binaries/standalone_xml.ts b/lib/binaries/standalone_xml.ts
index a9d8b18e..4e864f63 100644
--- a/lib/binaries/standalone_xml.ts
+++ b/lib/binaries/standalone_xml.ts
@@ -36,7 +36,7 @@ export class StandaloneXml extends XmlConfigSource {
 
   private getLatestStandaloneVersion(): Promise<BinaryUrl> {
     return this.getVersionList().then(list => {
-      let standaloneVersion = null;
+      let standaloneVersion: string = null;
       let latest = '';
       let latestVersion = '';
       for (let item of list) {
@@ -65,7 +65,7 @@ export class StandaloneXml extends XmlConfigSource {
   private getSpecificStandaloneVersion(inputVersion: string): Promise<BinaryUrl> {
     return this.getVersionList().then(list => {
       let itemFound = '';
-      let standaloneVersion = null;
+      let standaloneVersion: string = null;
 
       for (let item of list) {
         // Get a semantic version.
diff --git a/lib/cmds/start.ts b/lib/cmds/start.ts
index 7551e068..c90bafd6 100644
--- a/lib/cmds/start.ts
+++ b/lib/cmds/start.ts
@@ -289,7 +289,7 @@ function startAndroid(
       avd + '-v' + sdk.versionCustom + '-wd-manager',
       '-netfast',
     ];
-    let portArg = null;
+    let portArg: number = null;
     if (!useSnapshots) {
       emuArgs = emuArgs.concat(['-no-snapshot-load', '-no-snapshot-save']);
     }
diff --git a/package.json b/package.json
index 4097b6b6..8b2af9fd 100644
--- a/package.json
+++ b/package.json
@@ -65,7 +65,7 @@
     "jasmine": "^2.4.1",
     "run-sequence": "^1.1.5",
     "selenium-webdriver": "~3.0.1",
-    "typescript": "^2.1.1"
+    "typescript": "~2.0.0"
   },
   "engines": {
     "node": ">=6.9.x"