diff --git a/oauth2.go b/oauth2.go
index 291df5c83..951691bca 100644
--- a/oauth2.go
+++ b/oauth2.go
@@ -298,7 +298,7 @@ type reuseTokenSource struct {
 func (s *reuseTokenSource) Token() (*Token, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	if s.t.Valid() {
+	if s.t != nil && s.t.Valid() {
 		return s.t, nil
 	}
 	t, err := s.new.Token()