diff --git a/src/authorization_server.ts b/src/authorization_server.ts
index 07e6038c..d9df4ca7 100644
--- a/src/authorization_server.ts
+++ b/src/authorization_server.ts
@@ -104,6 +104,7 @@ export class AuthorizationServer {
       refresh_token: new RefreshTokenGrant(...grantProps),
       implicit: new ImplicitGrant(...grantProps),
     };
+    this.enableGrantTypes("client_credentials", "refresh_token");
   }
 
   enableGrantTypes(...grants: EnableGrant[]): void {
diff --git a/test/e2e/authorization_server.spec.ts b/test/e2e/authorization_server.spec.ts
index e0eb515c..1f5ab4fd 100644
--- a/test/e2e/authorization_server.spec.ts
+++ b/test/e2e/authorization_server.spec.ts
@@ -69,13 +69,11 @@ describe("authorization_server", () => {
       authCodeRepository: inMemoryAuthCodeRepository,
       userRepository: inMemoryUserRepository,
     });
-    authorizationServer.enableGrantType("client_credentials");
     authorizationServer.enableGrantType("implicit");
     authorizationServer.enableGrantType({
       grant: "password",
       userRepository: inMemoryUserRepository,
     });
-    authorizationServer.enableGrantType("refresh_token");
     const customGrant = new MyCustomGrant(
       inMemoryClientRepository,
       inMemoryAccessTokenRepository,
@@ -202,7 +200,6 @@ describe("authorization_server", () => {
       inMemoryScopeRepository,
       new JwtService("secret-key"),
     );
-    authorizationServer.enableGrantType("refresh_token");
     const request = new OAuthRequest({
       query: {
         response_type: "code",