diff --git a/cartographer/mapping_3d/submaps.cc b/cartographer/mapping_3d/submaps.cc
index 5568f49..c8fe152 100644
--- a/cartographer/mapping_3d/submaps.cc
+++ b/cartographer/mapping_3d/submaps.cc
@@ -200,13 +200,17 @@ proto::SubmapsOptions CreateSubmapsOptions(
 Submap::Submap(const float high_resolution, const float low_resolution,
                const transform::Rigid3d& local_submap_pose)
     : mapping::Submap(local_submap_pose),
-      high_resolution_hybrid_grid_(high_resolution),
-      low_resolution_hybrid_grid_(low_resolution) {}
+      high_resolution_hybrid_grid_(
+          common::make_unique<HybridGrid>(high_resolution)),
+      low_resolution_hybrid_grid_(
+          common::make_unique<HybridGrid>(low_resolution)) {}
 
 Submap::Submap(const mapping::proto::Submap3D& proto)
     : mapping::Submap(transform::ToRigid3(proto.local_pose())),
-      high_resolution_hybrid_grid_(proto.high_resolution_hybrid_grid()),
-      low_resolution_hybrid_grid_(proto.low_resolution_hybrid_grid()) {
+      high_resolution_hybrid_grid_(
+          common::make_unique<HybridGrid>(proto.high_resolution_hybrid_grid())),
+      low_resolution_hybrid_grid_(
+          common::make_unique<HybridGrid>(proto.low_resolution_hybrid_grid())) {
   SetNumRangeData(proto.num_range_data());
   finished_ = proto.finished();
 }
@@ -227,9 +231,9 @@ void Submap::ToResponseProto(
     mapping::proto::SubmapQuery::Response* const response) const {
   response->set_submap_version(num_range_data());
 
-  AddToTextureProto(high_resolution_hybrid_grid_, global_submap_pose,
+  AddToTextureProto(*high_resolution_hybrid_grid_, global_submap_pose,
                     response->add_textures());
-  AddToTextureProto(low_resolution_hybrid_grid_, global_submap_pose,
+  AddToTextureProto(*low_resolution_hybrid_grid_, global_submap_pose,
                     response->add_textures());
 }
 
@@ -242,9 +246,9 @@ void Submap::InsertRangeData(const sensor::RangeData& range_data,
   range_data_inserter.Insert(
       FilterRangeDataByMaxRange(transformed_range_data,
                                 high_resolution_max_range),
-      &high_resolution_hybrid_grid_);
+      high_resolution_hybrid_grid_.get());
   range_data_inserter.Insert(transformed_range_data,
-                             &low_resolution_hybrid_grid_);
+                             low_resolution_hybrid_grid_.get());
   SetNumRangeData(num_range_data() + 1);
 }
 
diff --git a/cartographer/mapping_3d/submaps.h b/cartographer/mapping_3d/submaps.h
index d8ce26d..ac94ee0 100644
--- a/cartographer/mapping_3d/submaps.h
+++ b/cartographer/mapping_3d/submaps.h
@@ -50,10 +50,10 @@ class Submap : public mapping::Submap {
   void ToProto(mapping::proto::Submap* proto) const override;
 
   const HybridGrid& high_resolution_hybrid_grid() const {
-    return high_resolution_hybrid_grid_;
+    return *high_resolution_hybrid_grid_;
   }
   const HybridGrid& low_resolution_hybrid_grid() const {
-    return low_resolution_hybrid_grid_;
+    return *low_resolution_hybrid_grid_;
   }
   bool finished() const { return finished_; }
 
@@ -69,8 +69,8 @@ class Submap : public mapping::Submap {
   void Finish();
 
  private:
-  HybridGrid high_resolution_hybrid_grid_;
-  HybridGrid low_resolution_hybrid_grid_;
+  std::unique_ptr<HybridGrid> high_resolution_hybrid_grid_;
+  std::unique_ptr<HybridGrid> low_resolution_hybrid_grid_;
   bool finished_ = false;
 };