diff --git a/cartographer/mapping/internal/2d/pose_graph_2d.cc b/cartographer/mapping/internal/2d/pose_graph_2d.cc
index 185d3f6..7827fc4 100644
--- a/cartographer/mapping/internal/2d/pose_graph_2d.cc
+++ b/cartographer/mapping/internal/2d/pose_graph_2d.cc
@@ -616,6 +616,7 @@ MapById<NodeId, TrajectoryNodePose> PoseGraph2D::GetTrajectoryNodePoses() {
 
 std::map<std::string, transform::Rigid3d> PoseGraph2D::GetLandmarkPoses() {
   std::map<std::string, transform::Rigid3d> landmark_poses;
+  common::MutexLocker locker(&mutex_);
   for (const auto& landmark : landmark_nodes_) {
     // Landmark without value has not been optimized yet.
     if (!landmark.second.global_landmark_pose.has_value()) continue;
diff --git a/cartographer/mapping/internal/3d/pose_graph_3d.cc b/cartographer/mapping/internal/3d/pose_graph_3d.cc
index ae1463f..8fb1dc6 100644
--- a/cartographer/mapping/internal/3d/pose_graph_3d.cc
+++ b/cartographer/mapping/internal/3d/pose_graph_3d.cc
@@ -659,6 +659,7 @@ MapById<NodeId, TrajectoryNodePose> PoseGraph3D::GetTrajectoryNodePoses() {
 
 std::map<std::string, transform::Rigid3d> PoseGraph3D::GetLandmarkPoses() {
   std::map<std::string, transform::Rigid3d> landmark_poses;
+  common::MutexLocker locker(&mutex_);
   for (const auto& landmark : landmark_nodes_) {
     // Landmark without value has not been optimized yet.
     if (!landmark.second.global_landmark_pose.has_value()) continue;