diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index 25ca508abd..4c0069bfb4 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -1142,7 +1142,7 @@ class cpp_function : public function {
                     }
                     msg += "kwargs: ";
                     bool first = true;
-                    for (auto kwarg : kwargs) {
+                    for (const auto &kwarg : kwargs) {
                         if (first) {
                             first = false;
                         } else {