diff --git a/google/default.go b/google/default.go
index a144d78..db6b19e 100644
--- a/google/default.go
+++ b/google/default.go
@@ -62,6 +62,10 @@ type CredentialsParams struct {
 
 	// PKCE is used to support PKCE flow. Optional for 3LO flow.
 	PKCE *authhandler.PKCEParams
+
+	// The OAuth2 TokenURL default override. This value overrides the default TokenURL,
+	// unless explicitly specified by the credentials config file. Optional.
+	TokenURL string
 }
 
 func (params CredentialsParams) deepCopy() CredentialsParams {
diff --git a/google/google.go b/google/google.go
index 8df0c49..a1b629a 100644
--- a/google/google.go
+++ b/google/google.go
@@ -26,6 +26,9 @@ var Endpoint = oauth2.Endpoint{
 	AuthStyle: oauth2.AuthStyleInParams,
 }
 
+// MTLSTokenURL is Google's OAuth 2.0 default mTLS endpoint.
+const MTLSTokenURL = "https://oauth2.mtls.googleapis.com/token"
+
 // JWTTokenURL is Google's OAuth 2.0 token URL to use with the JWT flow.
 const JWTTokenURL = "https://oauth2.googleapis.com/token"
 
@@ -172,7 +175,11 @@ func (f *credentialsFile) tokenSource(ctx context.Context, params CredentialsPar
 			cfg.Endpoint.AuthURL = Endpoint.AuthURL
 		}
 		if cfg.Endpoint.TokenURL == "" {
-			cfg.Endpoint.TokenURL = Endpoint.TokenURL
+			if params.TokenURL != "" {
+				cfg.Endpoint.TokenURL = params.TokenURL
+			} else {
+				cfg.Endpoint.TokenURL = Endpoint.TokenURL
+			}
 		}
 		tok := &oauth2.Token{RefreshToken: f.RefreshToken}
 		return cfg.TokenSource(ctx, tok), nil