diff --git a/python/ray/tests/test_basic.py b/python/ray/tests/test_basic.py
index 7140f393c..d1f84358e 100644
--- a/python/ray/tests/test_basic.py
+++ b/python/ray/tests/test_basic.py
@@ -1731,6 +1731,35 @@ def test_wait(ray_start_regular):
         ray.wait([1])
 
 
+def test_duplicate_args(ray_start_regular):
+    @ray.remote
+    def f(arg1,
+          arg2,
+          arg1_duplicate,
+          kwarg1=None,
+          kwarg2=None,
+          kwarg1_duplicate=None):
+        assert arg1 == kwarg1
+        assert arg1 != arg2
+        assert arg1 == arg1_duplicate
+        assert kwarg1 != kwarg2
+        assert kwarg1 == kwarg1_duplicate
+
+    # Test by-value arguments.
+    arg1 = [1]
+    arg2 = [2]
+    ray.get(
+        f.remote(
+            arg1, arg2, arg1, kwarg1=arg1, kwarg2=arg2, kwarg1_duplicate=arg1))
+
+    # Test by-reference arguments.
+    arg1 = ray.put([1])
+    arg2 = ray.put([2])
+    ray.get(
+        f.remote(
+            arg1, arg2, arg1, kwarg1=arg1, kwarg2=arg2, kwarg1_duplicate=arg1))
+
+
 if __name__ == "__main__":
     import pytest
     sys.exit(pytest.main(["-v", __file__]))
diff --git a/src/ray/core_worker/core_worker.cc b/src/ray/core_worker/core_worker.cc
index 743d08a09..ec41da335 100644
--- a/src/ray/core_worker/core_worker.cc
+++ b/src/ray/core_worker/core_worker.cc
@@ -1102,7 +1102,7 @@ Status CoreWorker::BuildArgsForExecutor(const TaskSpecification &task,
   arg_reference_ids->resize(num_args);
 
   absl::flat_hash_set<ObjectID> by_ref_ids;
-  absl::flat_hash_map<ObjectID, int> by_ref_indices;
+  absl::flat_hash_map<ObjectID, std::vector<size_t>> by_ref_indices;
 
   for (size_t i = 0; i < task.NumArgs(); ++i) {
     if (task.ArgByRef(i)) {
@@ -1117,7 +1117,12 @@ Status CoreWorker::BuildArgsForExecutor(const TaskSpecification &task,
       }
       const auto &arg_id = task.ArgId(i, 0);
       by_ref_ids.insert(arg_id);
-      by_ref_indices.emplace(arg_id, i);
+      auto it = by_ref_indices.find(arg_id);
+      if (it == by_ref_indices.end()) {
+        by_ref_indices.emplace(arg_id, std::vector<size_t>({i}));
+      } else {
+        it->second.push_back(i);
+      }
       arg_reference_ids->at(i) = arg_id;
       // The task borrows all args passed by reference. Because the task does
       // not have a reference to the argument ID in the frontend, it is not
@@ -1155,7 +1160,9 @@ Status CoreWorker::BuildArgsForExecutor(const TaskSpecification &task,
   RAY_RETURN_NOT_OK(plasma_store_provider_->Get(by_ref_ids, -1, worker_context_,
                                                 &result_map, &got_exception));
   for (const auto &it : result_map) {
-    args->at(by_ref_indices[it.first]) = it.second;
+    for (size_t idx : by_ref_indices[it.first]) {
+      args->at(idx) = it.second;
+    }
   }
 
   return Status::OK();