diff --git a/plugin/auth/oauth.go b/plugin/auth/oauth.go
index 1785459b2..48f14f6f6 100644
--- a/plugin/auth/oauth.go
+++ b/plugin/auth/oauth.go
@@ -88,8 +88,9 @@ func NewOauthFromConfig(ctx context.Context, other map[string]any) (oauth2.Token
 }
 
 var _ api.AuthProvider = (*OAuth)(nil)
+var _ oauth2.TokenSource = (*OAuth)(nil)
 
-func NewOauth(ctx context.Context, name, device string, oc *oauth2.Config, opts ...oauthOption) (oauth2.TokenSource, error) {
+func NewOauth(ctx context.Context, name, device string, oc *oauth2.Config, opts ...oauthOption) (*OAuth, error) {
 	if name == "" {
 		return nil, errors.New("instance name must not be empty")
 	}