diff --git a/cpp/include/raft/neighbors/ivf_flat_types.hpp b/cpp/include/raft/neighbors/ivf_flat_types.hpp
index ccdc3f28da..2e2e49cdbc 100644
--- a/cpp/include/raft/neighbors/ivf_flat_types.hpp
+++ b/cpp/include/raft/neighbors/ivf_flat_types.hpp
@@ -23,15 +23,18 @@
 #include <raft/core/error.hpp>
 #include <raft/core/host_mdarray.hpp>
 #include <raft/core/mdspan_types.hpp>
+#include <raft/core/operators.hpp>
+#include <raft/core/resource/thrust_policy.hpp>
 #include <raft/core/resources.hpp>
 #include <raft/distance/distance_types.hpp>
 #include <raft/neighbors/ivf_list_types.hpp>
 #include <raft/util/integer_utils.hpp>
 
+#include <thrust/reduce.h>
+
 #include <algorithm>  // std::max
 #include <memory>
 #include <optional>
-#include <thrust/fill.h>
 #include <type_traits>
 
 namespace raft::neighbors::ivf_flat {
@@ -303,20 +306,22 @@ struct index : ann::index {
     auto stream = resource::get_cuda_stream(res);
 
     // Actualize the list pointers
-    auto this_lists           = lists();
-    auto this_data_ptrs       = data_ptrs();
-    auto this_inds_ptrs       = inds_ptrs();
-    IdxT recompute_total_size = 0;
+    auto this_lists     = lists();
+    auto this_data_ptrs = data_ptrs();
+    auto this_inds_ptrs = inds_ptrs();
     for (uint32_t label = 0; label < this_lists.size(); label++) {
-      auto& list           = this_lists[label];
-      const auto data_ptr  = list ? list->data.data_handle() : nullptr;
-      const auto inds_ptr  = list ? list->indices.data_handle() : nullptr;
-      const auto list_size = list ? IdxT(list->size) : 0;
+      auto& list          = this_lists[label];
+      const auto data_ptr = list ? list->data.data_handle() : nullptr;
+      const auto inds_ptr = list ? list->indices.data_handle() : nullptr;
       copy(&this_data_ptrs(label), &data_ptr, 1, stream);
       copy(&this_inds_ptrs(label), &inds_ptr, 1, stream);
-      recompute_total_size += list_size;
     }
-    total_size_ = recompute_total_size;
+    auto this_list_sizes = list_sizes().data_handle();
+    total_size_          = thrust::reduce(resource::get_thrust_policy(res),
+                                 this_list_sizes,
+                                 this_list_sizes + this_lists.size(),
+                                 0,
+                                 raft::add_op{});
     check_consistency();
   }
 
diff --git a/cpp/test/neighbors/ann_ivf_flat.cuh b/cpp/test/neighbors/ann_ivf_flat.cuh
index 1c9406e8a9..88bf53280b 100644
--- a/cpp/test/neighbors/ann_ivf_flat.cuh
+++ b/cpp/test/neighbors/ann_ivf_flat.cuh
@@ -201,6 +201,7 @@ class AnnIVFFlatTest : public ::testing::TestWithParam<AnnIvfFlatInputs<IdxT>> {
         ivf_flat::detail::serialize(handle_, "ivf_flat_index", index_2);
 
         auto index_loaded = ivf_flat::detail::deserialize<DataT, IdxT>(handle_, "ivf_flat_index");
+        ASSERT_EQ(index_2.size(), index_loaded.size());
 
         ivf_flat::search(handle_,
                          search_params,