diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h
index 93c8238c5..cd54de285 100644
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
@@ -473,8 +473,10 @@ PYBIND11_NOINLINE bool isinstance_generic(handle obj, const std::type_info &tp)
 PYBIND11_NOINLINE std::string
 error_string(PyObject *exc_type, PyObject *exc_value, PyObject *exc_trace) {
     if (!exc_type) {
-        PyErr_SetString(PyExc_RuntimeError, "Unknown internal error occurred");
-        return "Unknown internal error occurred";
+        static const char *msg
+            = "Internal error: error_string() called without a Python error available.";
+        PyErr_SetString(PyExc_RuntimeError, msg);
+        return msg;
     }
 
     auto result = handle(exc_type).attr("__name__").cast<std::string>();
diff --git a/tests/test_exceptions.cpp b/tests/test_exceptions.cpp
index 3e9a3d771..99eaed36a 100644
--- a/tests/test_exceptions.cpp
+++ b/tests/test_exceptions.cpp
@@ -228,7 +228,10 @@ TEST_SUBMODULE(exceptions, m) {
             throw py::error_already_set();
         } catch (const std::runtime_error &e) {
             if ((err && e.what() != std::string("ValueError: foo"))
-                || (!err && e.what() != std::string("Unknown internal error occurred"))) {
+                || (!err
+                    && e.what()
+                           != std::string("Internal error: error_string() called without a Python "
+                                          "error available."))) {
                 PyErr_Clear();
                 throw std::runtime_error("error message mismatch");
             }