diff --git a/.gitignore b/.gitignore
index 46a7572..b2b54e8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,4 +6,5 @@ prop-types.js
 yarn.lock
 shrinkwrap.yaml
 coverage.lcov
-/remove.js
\ No newline at end of file
+/remove.js
+types/*.js
\ No newline at end of file
diff --git a/jest.config.js b/jest.config.js
new file mode 100644
index 0000000..f6c0e8d
--- /dev/null
+++ b/jest.config.js
@@ -0,0 +1,3 @@
+module.exports = {
+  testMatch: ['<rootDir>/test/*.spec.js']
+}
\ No newline at end of file
diff --git a/jsconfig.json b/jsconfig.json
new file mode 100644
index 0000000..75d2ecb
--- /dev/null
+++ b/jsconfig.json
@@ -0,0 +1,8 @@
+{
+  "include": ["src"],
+  "exclude": ["node_modules"],
+  "compilerOptions": {
+    "resolveJsonModule": true,
+    "lib": ["esnext"]
+  }
+}
diff --git a/package.json b/package.json
index a8157a4..d138c8f 100644
--- a/package.json
+++ b/package.json
@@ -12,7 +12,9 @@
     "remove.js"
   ],
   "scripts": {
-    "test": "jest",
+    "test": "npm run test:unit && npm run test:types",
+    "test:unit": "jest",
+    "test:types": "tsc types/index.spec.ts",
     "pre:build": "rm -rf dist/",
     ":build": "rollup -c --environment BUILD:production",
     "prepublishOnly": "npm run :build",
@@ -40,12 +42,12 @@
     "@babel/core": "^7.2.2",
     "@babel/preset-env": "^7.2.3",
     "babel-core": "^7.0.0-bridge.0",
-    "babel-jest": "^23.6.0",
-    "jest": "^23.6.0",
-    "regenerator-runtime": "^0.13.1",
+    "babel-jest": "^24.1.0",
+    "jest": "^24.1.0",
     "rollup": "^1.1.0",
     "rollup-plugin-babel": "^4.3.1",
-    "standard-version": "^4.4.0"
+    "standard-version": "^4.4.0",
+    "typescript": "^3.3.3"
   },
   "dependencies": {
     "vue": "2.*"
diff --git a/types/index.d.ts b/types/index.d.ts
index 96c694d..3baa43a 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -36,9 +36,9 @@ export interface PropTypes {
   arrayOf<T>(type: ValidatorFn<T>): PropValidator<Array<T>>
 
   oneOf<T>(...args: T[]): PropValidator<T>
-  oneOf<T1>(arg1: T1): PropValidator<T1 | T2 | T3 | T4>
-  oneOf<T1, T2>(arg1: T1, arg2: T2): PropValidator<T1 | T2 | T3 | T4>
-  oneOf<T1, T2, T3>(arg1: T1, arg2: T2, arg3: T3): PropValidator<T1 | T2 | T3 | T4>
+  oneOf<T1>(arg1: T1): PropValidator<T1>
+  oneOf<T1, T2>(arg1: T1, arg2: T2): PropValidator<T1 | T2>
+  oneOf<T1, T2, T3>(arg1: T1, arg2: T2, arg3: T3): PropValidator<T1 | T2 | T3>
   oneOf<T1, T2, T3, T4>(arg1: T1, arg2: T2, arg3: T3, arg4: T4): PropValidator<T1 | T2 | T3 | T4>
   oneOf<T1, T2, T3, T4, T5>(arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5): PropValidator<T1 | T2 | T3 | T4 | T5>
   oneOf<T1, T2, T3, T4, T5, T6>(arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, arg6: T6): PropValidator<T1 | T2 | T3 | T4 | T5 | T6>
@@ -89,20 +89,20 @@ export interface PropTypesChain<
   T,
   U = T extends string
     ? string
-    : T extends StringConstructor
+    : T extends String
     ? string
     : T extends number
     ? number
-    : T extends NumberConstructor
+    : T extends Number
     ? number
     : T extends boolean
     ? boolean
-    : T extends BooleanConstructor
+    : T extends Boolean
     ? boolean
+    : T extends symbol
+    ? symbol
     : T extends Symbol
-    ? Symbol
-    : T extends SymbolConstructor
-    ? Symbol
+    ? symbol
     : (() => T)
 > {
   isRequired: PropOptions<T>
diff --git a/types/index.spec.ts b/types/index.spec.ts
index 3c89281..159bdb9 100644
--- a/types/index.spec.ts
+++ b/types/index.spec.ts
@@ -9,7 +9,6 @@ const props = {
   string: PropTypes.string.value('foo').validate(value => 'foo' == value).isRequired,
   number: PropTypes.number.value(1).validate(value => 1 == value).isRequired,
   boolean: PropTypes.bool.value(true).validate(value => value).isRequired,
-  symbol: PropTypes.symbol.value(Symbol('1')).validate(value => !!value).isRequired,
   array: PropTypes.array.value(() => []).validate(value => 1 === value.length).isRequired,
   object: PropTypes.object.value(() => ({})).validate(value => 'foo' in value).isRequired,
   func: PropTypes.func.value(() => (a: string) => null).validate(value => value()).isRequired,
@@ -24,7 +23,7 @@ const props = {
   
   date: PropTypes.instanceOf(Date).value(() => new Date()).validate(value => value.getTime() > 0).isRequired,
   foo: PropTypes.instanceOf(Foo).value(() => new Foo()).validate(value => value.isValid).isRequired,
-  String: PropTypes.instanceOf(String).value(() => new String()).validate(value => value.at(0) > 'a').isRequired,
+  String: PropTypes.instanceOf(String).value(String('str')).validate(value => value.charAt(0) > 'a').isRequired,
 
   shape: PropTypes.shape({
     foo: PropTypes.bool,
@@ -34,7 +33,6 @@ const props = {
 
   objectOfNumber: PropTypes.objectOf(PropTypes.number).value(() => ({ foo: 1, bar: 2 })).validate(value => value.foo > 0).isRequired,
   objectOfString: PropTypes.objectOf(Number),
-  objectOfSymbol: PropTypes.objectOf(Symbol),
   objectOfValidatorInferredType: PropTypes.objectOf((value: { foo: boolean}) => value.foo).value(() => ({ one: { foo: true } })),
 }