diff --git a/lib/oidc/endpoints/token.ts b/lib/oidc/endpoints/token.ts
index 76e0f25d8..8a257a5cc 100644
--- a/lib/oidc/endpoints/token.ts
+++ b/lib/oidc/endpoints/token.ts
@@ -131,24 +131,23 @@ export async function postRefreshToken(
   options: TokenEndpointParams,
   refreshToken: RefreshToken
 ): Promise<OAuthResponse> {
-  let requestParams = {
+  const data = Object.entries({
     client_id: options.clientId, // eslint-disable-line camelcase
     grant_type: 'refresh_token', // eslint-disable-line camelcase
     scope: refreshToken.scopes.join(' '),
     refresh_token: refreshToken.refreshToken, // eslint-disable-line camelcase
-  };
-
-  if (options.extraParams) {
-    requestParams = { ...options.extraParams, ...requestParams };
-  }
-
-  const data = Object.entries(requestParams).map(function ([name, value]) {
+  }).map(function ([name, value]) {
     // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
     return name + '=' + encodeURIComponent(value!);
   }).join('&');
 
+  let url = refreshToken.tokenUrl;
+  if (options.extraParams && Object.keys(options.extraParams).length >= 1) {
+    url += toQueryString(options.extraParams);
+  }
+
   const params: TokenRequestParams = {
-    url: refreshToken.tokenUrl,
+    url,
     data,
     dpopKeyPair: options?.dpopKeyPair
   };
diff --git a/test/spec/oidc/endpoints/token.ts b/test/spec/oidc/endpoints/token.ts
index 1651c6c11..507b30501 100644
--- a/test/spec/oidc/endpoints/token.ts
+++ b/test/spec/oidc/endpoints/token.ts
@@ -57,7 +57,6 @@ describe('token endpoint', function() {
               client_id: CLIENT_ID,
               grant_type: 'authorization_code',
               redirect_uri: REDIRECT_URI,
-              extraParams: extraParams
             },
             headers: {
               'Accept': 'application/json',
@@ -82,8 +81,7 @@ describe('token endpoint', function() {
         clientId: CLIENT_ID,
         redirectUri: REDIRECT_URI,
         authorizationCode: authorizationCode,
-        codeVerifier: codeVerifier,
-        extraParams: extraParams
+        codeVerifier: codeVerifier
       }, {
         tokenUrl: ISSUER + endpoint
       });
@@ -159,6 +157,37 @@ describe('token endpoint', function() {
 
   });
 
+  describe('postRefreshToken', () => {
+    var authClient;
+    var oauthOptions;
+
+    beforeEach(function() {
+      spyOn(OktaAuth.features, 'isPKCESupported').and.returnValue(true);
+      authClient = new OktaAuth({
+        issuer: 'https://auth-js-test.okta.com'
+      });
+
+      oauthOptions = {
+        clientId: CLIENT_ID,
+        redirectUri: REDIRECT_URI,
+        authorizationCode: authorizationCode,
+        codeVerifier: codeVerifier,
+      };
+    });
+
+    it('should append extra params as query params', async () => {
+      var httpRequest = jest.spyOn(mocked.http, 'httpRequest').mockImplementation();
+      const refreshToken = tokens.standardRefreshTokenParsed;
+      await postRefreshToken(authClient, { extraParams }, refreshToken);
+      expect(httpRequest).toHaveBeenCalled();
+      expect(httpRequest).toHaveBeenLastCalledWith(expect.any(OktaAuth), expect.objectContaining({
+        url: 'https://auth-js-test.okta.com/oauth2/v1/token?foo=bar',
+        method: 'POST',
+        headers: {'Content-Type': 'application/x-www-form-urlencoded' }
+      }));
+    });
+  });
+
   describe('dpop', () => {
     const ctx: any = {};