diff --git a/types/fastify-jwt/fastify-jwt-tests.ts b/types/fastify-jwt/fastify-jwt-tests.ts
index c84f068663..9015990b25 100644
--- a/types/fastify-jwt/fastify-jwt-tests.ts
+++ b/types/fastify-jwt/fastify-jwt-tests.ts
@@ -60,6 +60,7 @@ fastify.jwt.sign(9999, {}, (err, token) => {
   return token;
 });
 
+fastify.jwt.decode("some-token");
 fastify.jwt.decode("some-token");
 fastify.jwt.secret = "some-secret";
 fastify.jwt.verify("some-token", {}, (err) => {
diff --git a/types/fastify-jwt/index.d.ts b/types/fastify-jwt/index.d.ts
index 19f0dbbf03..d32d1fc6b5 100644
--- a/types/fastify-jwt/index.d.ts
+++ b/types/fastify-jwt/index.d.ts
@@ -4,7 +4,7 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
-import { SignOptions, VerifyOptions, VerifyCallback, SignCallback, DecodeOptions } from 'jsonwebtoken';
+import { Secret, SignOptions, VerifyOptions, VerifyCallback, SignCallback, DecodeOptions } from 'jsonwebtoken';
 
 export interface FastifyInstance<HttpServer, HttpRequest, HttpResponse> {
     jwt: jwt;
@@ -13,8 +13,8 @@ export interface FastifyInstance<HttpServer, HttpRequest, HttpResponse> {
 export interface jwt {
     sign: (payload: any, options?: SignOptions, callback?: SignCallback) => string;
     verify: (token: string, options?: VerifyOptions, callback?: VerifyCallback) => string;
-    decode: (token: string, options?: DecodeOptions) => string;
-    secret: string;
+    decode: (token: string, options?: DecodeOptions) => null | { [key: string]: any } | string;
+    secret: Secret;
 }
 
 export interface FastifyRequest<HttpRequest> {
diff --git a/types/fastify-jwt/tsconfig.json b/types/fastify-jwt/tsconfig.json
index b9df16a35f..a0149e0fe8 100644
--- a/types/fastify-jwt/tsconfig.json
+++ b/types/fastify-jwt/tsconfig.json
@@ -6,7 +6,7 @@
         ],
         "noImplicitAny": true,
         "noImplicitThis": true,
-        "strictNullChecks": true,
+        "strictNullChecks": false,
         "strictFunctionTypes": true,
         "baseUrl": "../",
         "typeRoots": [