diff --git a/python/google/protobuf/pyext/repeated_scalar_container.cc b/python/google/protobuf/pyext/repeated_scalar_container.cc
index edbb75d4d0..8cf236bf7a 100644
--- a/python/google/protobuf/pyext/repeated_scalar_container.cc
+++ b/python/google/protobuf/pyext/repeated_scalar_container.cc
@@ -57,6 +57,7 @@ namespace repeated_scalar_container {
 
 static int InternalAssignRepeatedField(RepeatedScalarContainer* self,
                                        PyObject* list) {
+  cmessage::AssureWritable(self->parent);
   Message* message = self->parent->message;
   message->GetReflection()->ClearField(message, self->parent_field_descriptor);
   for (Py_ssize_t i = 0; i < PyList_GET_SIZE(list); ++i) {
@@ -589,6 +590,9 @@ static PyObject* Sort(PyObject* pself, PyObject* args, PyObject* kwds) {
   if (list == nullptr) {
     return nullptr;
   }
+  if (PyList_GET_SIZE(list.get()) == 0) {
+    Py_RETURN_NONE;
+  }
   ScopedPyObjectPtr m(PyObject_GetAttrString(list.get(), "sort"));
   if (m == nullptr) {
     return nullptr;