diff --git a/packages/auth0-fastify-api/src/index.spec.ts b/packages/auth0-fastify-api/src/index.spec.ts
index 25d0fd3..1c6f42c 100644
--- a/packages/auth0-fastify-api/src/index.spec.ts
+++ b/packages/auth0-fastify-api/src/index.spec.ts
@@ -53,7 +53,7 @@ afterEach(() => {
   server.resetHandlers();
 });
 
-test('should return 400 when no token', async () => {
+test('should return 401 when no authorization header', async () => {
   const fastify = Fastify();
   fastify.register(fastifyAuth0Api, {
     domain: domain,
@@ -77,9 +77,43 @@ test('should return 400 when no token', async () => {
     url: '/test',
   });
 
-  expect(res.statusCode).toBe(400);
+  expect(res.statusCode).toBe(401);
   expect(res.json().error).toBe('invalid_request');
   expect(res.json().error_description).toBe('No Authorization provided');
+  expect(res.headers['www-authenticate']).toBe('Bearer');
+});
+
+test('should return 400 when invalid authorization header', async () => {
+  const fastify = Fastify();
+  fastify.register(fastifyAuth0Api, {
+    domain: domain,
+    audience: '<audience>',
+  });
+
+  fastify.register(() => {
+    fastify.get(
+      '/test',
+      {
+        preHandler: fastify.requireAuth(),
+      },
+      async () => {
+        return 'OK';
+      }
+    );
+  });
+
+  const res = await fastify.inject({
+    method: 'GET',
+    url: '/test',
+    headers: {
+      authorization: 'Bearer'
+    }
+  });
+
+  expect(res.statusCode).toBe(400);
+  expect(res.json().error).toBe('invalid_request');
+  expect(res.json().error_description).toBe('Invalid Authorization provided');
+  expect(res.headers['www-authenticate']).toBe('Bearer error="invalid_request", error_description="Invalid Authorization provided"');
 });
 
 test('should return 200 when valid token', async () => {
diff --git a/packages/auth0-fastify-api/src/index.ts b/packages/auth0-fastify-api/src/index.ts
index 3ef7ea5..310a768 100644
--- a/packages/auth0-fastify-api/src/index.ts
+++ b/packages/auth0-fastify-api/src/index.ts
@@ -65,25 +65,41 @@ async function auth0FastifApi(fastify: FastifyInstance, options: Auth0FastifyApi
     customFetch: options.customFetch,
   });
 
-  const replyWithError = (reply: FastifyReply, statusCode: number, error: string, errorDescription: string) => {
-    return reply
-      .code(statusCode)
-      .header(
-        'WWW-Authenticate',
-        `Bearer error="${error.replaceAll('"', '\\"')}", error_description="${errorDescription.replaceAll('"', '\\"')}"`
-      )
-      .send({
-        error: error,
-        error_description: errorDescription,
-      });
+  const replyWithError = (
+    reply: FastifyReply,
+    statusCode: number,
+    error: string,
+    errorDescription: string,
+    ommitHeaderDetails = false
+  ) => {
+    const headerValue = ommitHeaderDetails
+      ? `Bearer`
+      : `Bearer error="${error.replaceAll('"', '\\"')}", error_description="${errorDescription.replaceAll(
+          '"',
+          '\\"'
+        )}"`;
+
+    return reply.code(statusCode).header('WWW-Authenticate', headerValue).send({
+      error: error,
+      error_description: errorDescription,
+    });
   };
 
   fastify.decorate('requireAuth', function (opts: AuthRouteOptions = {}) {
     return async function (request: FastifyRequest, reply: FastifyReply) {
+      const authorizationHeader = request.headers.authorization;
+
+      if (!authorizationHeader) {
+        // If there is no authorization header,
+        // we need to return a 401 with just the supported scheme and no error/error_description in www-authenticate.
+        return replyWithError(reply, 401, 'invalid_request', 'No Authorization provided', true);
+      }
+
       const accessToken = getToken(request);
 
       if (!accessToken) {
-        return replyWithError(reply, 400, 'invalid_request', 'No Authorization provided');
+        // If the authorization header was malformed, we need to return a 400.
+        return replyWithError(reply, 400, 'invalid_request', 'Invalid Authorization provided');
       }
 
       try {
@@ -110,7 +126,6 @@ async function auth0FastifApi(fastify: FastifyInstance, options: Auth0FastifyApi
   });
 }
 
-
 export default fp(auth0FastifApi);
 
 function getToken(request: FastifyRequest): string | undefined {