diff --git a/cartographer/mapping/sparse_pose_graph.h b/cartographer/mapping/sparse_pose_graph.h
index a82eac8..c1c9fa0 100644
--- a/cartographer/mapping/sparse_pose_graph.h
+++ b/cartographer/mapping/sparse_pose_graph.h
@@ -99,10 +99,10 @@ class SparsePoseGraph {
   // Serializes the constraints and trajectories.
   proto::SparsePoseGraph ToProto();
 
- protected:
   // Returns the collection of constraints.
   virtual std::vector<Constraint> constraints() = 0;
 
+ protected:
   // Returns the mapping from Submaps* to trajectory IDs.
   virtual const std::unordered_map<const Submaps*, int>& trajectory_ids() = 0;
 };
diff --git a/cartographer/mapping_2d/sparse_pose_graph.h b/cartographer/mapping_2d/sparse_pose_graph.h
index 0c76acd..bb615ed 100644
--- a/cartographer/mapping_2d/sparse_pose_graph.h
+++ b/cartographer/mapping_2d/sparse_pose_graph.h
@@ -88,9 +88,9 @@ class SparsePoseGraph : public mapping::SparsePoseGraph {
       EXCLUDES(mutex_) override;
   std::vector<mapping::TrajectoryNode> GetTrajectoryNodes() override
       EXCLUDES(mutex_);
+  std::vector<Constraint> constraints() override EXCLUDES(mutex_);
 
  protected:
-  std::vector<Constraint> constraints() override EXCLUDES(mutex_);
   const std::unordered_map<const mapping::Submaps*, int>& trajectory_ids()
       override EXCLUDES(mutex_);
 
diff --git a/cartographer/mapping_3d/sparse_pose_graph.h b/cartographer/mapping_3d/sparse_pose_graph.h
index ae45126..807b6a9 100644
--- a/cartographer/mapping_3d/sparse_pose_graph.h
+++ b/cartographer/mapping_3d/sparse_pose_graph.h
@@ -90,9 +90,9 @@ class SparsePoseGraph : public mapping::SparsePoseGraph {
       EXCLUDES(mutex_) override;
   std::vector<mapping::TrajectoryNode> GetTrajectoryNodes() override
       EXCLUDES(mutex_);
+  std::vector<Constraint> constraints() override EXCLUDES(mutex_);
 
  protected:
-  std::vector<Constraint> constraints() override EXCLUDES(mutex_);
   const std::unordered_map<const mapping::Submaps*, int>& trajectory_ids()
       override EXCLUDES(mutex_);