diff --git a/cpp/include/cudf/detail/groupby/sort_helper.hpp b/cpp/include/cudf/detail/groupby/sort_helper.hpp
index 3a61e5d7114..294978bf128 100644
--- a/cpp/include/cudf/detail/groupby/sort_helper.hpp
+++ b/cpp/include/cudf/detail/groupby/sort_helper.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -99,7 +99,7 @@ struct sort_groupby_helper {
   /**
    * @brief Groups a column of values according to `keys`
    *
-   * The order of values within each group is undefined.
+   * The values within each group maintain their original order.
    *
    * @throw cudf::logic_error if `values.size() != keys.num_rows()`
    *
diff --git a/cpp/src/replace/nulls.cu b/cpp/src/replace/nulls.cu
index 5ce1a7af4ad..c78b1c67c04 100644
--- a/cpp/src/replace/nulls.cu
+++ b/cpp/src/replace/nulls.cu
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, NVIDIA CORPORATION.
+ * Copyright (c) 2020-2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -387,7 +387,7 @@ std::unique_ptr<cudf::column> replace_nulls_policy_impl(cudf::column_view const&
   auto valid_it  = cudf::detail::make_validity_iterator(*device_in);
   auto in_begin  = thrust::make_zip_iterator(thrust::make_tuple(index, valid_it));
 
-  rmm::device_vector<cudf::size_type> gather_map(input.size());
+  rmm::device_uvector<cudf::size_type> gather_map(input.size(), stream);
   auto gm_begin = thrust::make_zip_iterator(
     thrust::make_tuple(gather_map.begin(), thrust::make_discard_iterator()));
 
@@ -405,7 +405,8 @@ std::unique_ptr<cudf::column> replace_nulls_policy_impl(cudf::column_view const&
   auto output = cudf::detail::gather(cudf::table_view({input}),
                                      gather_map.begin(),
                                      gather_map.end(),
-                                     cudf::out_of_bounds_policy::DONT_CHECK);
+                                     cudf::out_of_bounds_policy::DONT_CHECK,
+                                     stream);
 
   return std::move(output->release()[0]);
 }