diff --git a/types/qs/index.d.ts b/types/qs/index.d.ts
index 400cc7a1e4..d3574383a5 100644
--- a/types/qs/index.d.ts
+++ b/types/qs/index.d.ts
@@ -1,7 +1,9 @@
-// Type definitions for qs 6.2.0
-// Project: https://github.com/hapijs/qs
-// Definitions by: Roman Korneev <https://github.com/RWander>, Leon Yu <https://github.com/leonyu>,
-//     Belinda Teh <https://github.com/tehbelinda>
+// Type definitions for qs 6.4.0
+// Project: https://github.com/ljharb/qs
+// Definitions by: Roman Korneev <https://github.com/RWander>
+//                 Leon Yu <https://github.com/leonyu>
+//                 Belinda Teh <https://github.com/tehbelinda>
+//                 Melvin Lee <https://github.com/zyml>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 export = QueryString;
@@ -18,6 +20,9 @@ declare namespace QueryString {
         arrayFormat?: 'indices' | 'brackets' | 'repeat';
         indices?: boolean;
         sort?: (a: any, b: any) => number;
+        serializeDate?: (d: Date) => string;
+        format?: 'RFC1738' | 'RFC3986';
+        encodeValuesOnly?: boolean;
     }
 
     interface IParseOptions {
diff --git a/types/qs/qs-tests.ts b/types/qs/qs-tests.ts
index f3e5ca3230..d71aa55957 100644
--- a/types/qs/qs-tests.ts
+++ b/types/qs/qs-tests.ts
@@ -254,3 +254,27 @@ qs.parse('a=b&c=d', { delimiter: '&' });
     var sorted = qs.stringify({ a: 1, c: 3, b: 2 }, { sort: (a, b) => a.localeCompare(b) })
     assert.equal(sorted, 'a=1&b=2&c=3')
 }
+
+() => {
+    var date = new Date(7);
+    assert.equal(
+        qs.stringify({ a: date }, { serializeDate: function (d) { return d.getTime().toString(); } }),
+        'a=7'
+    );
+}
+
+() => {
+    assert.equal(qs.stringify({ a: 'b c' }, { format : 'RFC3986' }), 'a=b%20c');
+}
+
+() => {
+    assert.equal(qs.stringify({ a: 'b c' }, { format : 'RFC1738' }), 'a=b+c');
+}
+
+() => {
+    var encodedValues = qs.stringify(
+        { a: 'b', c: ['d', 'e=f'], f: [['g'], ['h']] },
+        { encodeValuesOnly: true }
+    );
+    assert.equal(encodedValues,'a=b&c[0]=d&c[1]=e%3Df&f[0][0]=g&f[1][0]=h');
+}
diff --git a/types/qs/tsconfig.json b/types/qs/tsconfig.json
index 13f816338d..624bdc72f2 100644
--- a/types/qs/tsconfig.json
+++ b/types/qs/tsconfig.json
@@ -6,7 +6,7 @@
         ],
         "noImplicitAny": true,
         "noImplicitThis": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "baseUrl": "../",
         "typeRoots": [
             "../"
@@ -19,4 +19,4 @@
         "index.d.ts",
         "qs-tests.ts"
     ]
-}
\ No newline at end of file
+}