diff --git a/cartographer/mapping/internal/3d/pose_graph_3d.cc b/cartographer/mapping/internal/3d/pose_graph_3d.cc
index 196f276..3622ebc 100644
--- a/cartographer/mapping/internal/3d/pose_graph_3d.cc
+++ b/cartographer/mapping/internal/3d/pose_graph_3d.cc
@@ -51,7 +51,7 @@ PoseGraph3D::PoseGraph3D(
 
 PoseGraph3D::~PoseGraph3D() {
   WaitForAllComputations();
-  common::MutexLocker locker(&mutex_);
+  common::MutexLocker locker(&work_queue_mutex_);
   CHECK(work_queue_ == nullptr);
 }
 
@@ -153,7 +153,7 @@ NodeId PoseGraph3D::AddNode(
 void PoseGraph3D::AddWorkItem(
     const std::function<WorkItem::Result()>& work_item) {
   {
-    common::MutexLocker locker(&mutex_);
+    common::MutexLocker locker(&work_queue_mutex_);
     if (work_queue_ != nullptr) {
       const auto now = std::chrono::steady_clock::now();
       work_queue_->push_back({now, work_item});
@@ -164,7 +164,7 @@ void PoseGraph3D::AddWorkItem(
   }
   if (work_item() == WorkItem::Result::kRunOptimization) {
     {
-      common::MutexLocker locker(&mutex_);
+      common::MutexLocker locker(&work_queue_mutex_);
       work_queue_ = common::make_unique<WorkQueue>();
     }
     constraint_builder_.WhenDone(
@@ -489,7 +489,7 @@ void PoseGraph3D::HandleWorkQueue(
   while (process_work_queue) {
     std::function<WorkItem::Result()> work_item;
     {
-      common::MutexLocker locker(&mutex_);
+      common::MutexLocker locker(&work_queue_mutex_);
       if (work_queue_->empty()) {
         work_queue_.reset();
         return;
@@ -509,40 +509,60 @@ void PoseGraph3D::HandleWorkQueue(
 }
 
 void PoseGraph3D::WaitForAllComputations() {
-  bool notification = false;
-  common::MutexLocker locker(&mutex_);
+  int num_trajectory_nodes;
+  {
+    common::MutexLocker locker(&mutex_);
+    num_trajectory_nodes = data_.num_trajectory_nodes;
+  }
+
   const int num_finished_nodes_at_start =
       constraint_builder_.GetNumFinishedNodes();
-  while (!locker.AwaitWithTimeout(
-      [this]() REQUIRES(mutex_) {
-        return ((constraint_builder_.GetNumFinishedNodes() ==
-                 data_.num_trajectory_nodes) &&
-                !work_queue_);
-      },
-      common::FromSeconds(1.))) {
+
+  auto report_progress = [this, num_trajectory_nodes,
+                          num_finished_nodes_at_start]() {
     // Log progress on nodes only when we are actually processing nodes.
-    if (data_.num_trajectory_nodes != num_finished_nodes_at_start) {
+    if (num_trajectory_nodes != num_finished_nodes_at_start) {
       std::ostringstream progress_info;
       progress_info << "Optimizing: " << std::fixed << std::setprecision(1)
                     << 100. *
                            (constraint_builder_.GetNumFinishedNodes() -
                             num_finished_nodes_at_start) /
-                           (data_.num_trajectory_nodes -
-                            num_finished_nodes_at_start)
+                           (num_trajectory_nodes - num_finished_nodes_at_start)
                     << "%...";
       std::cout << "\r\x1b[K" << progress_info.str() << std::flush;
     }
+  };
+
+  // First wait for the work queue to drain so that it's safe to schedule
+  // a WhenDone() callback.
+  {
+    common::MutexLocker locker(&work_queue_mutex_);
+    while (!locker.AwaitWithTimeout(
+        [this]() REQUIRES(work_queue_mutex_) { return work_queue_ == nullptr; },
+        common::FromSeconds(1.))) {
+      report_progress();
+    }
   }
-  std::cout << "\r\x1b[KOptimizing: Done.     " << std::endl;
+
+  // Now wait for any pending constraint computations to finish.
+  common::MutexLocker locker(&mutex_);
+  bool notification GUARDED_BY(mutex_) = false;
   constraint_builder_.WhenDone(
       [this,
-       &notification](const constraints::ConstraintBuilder3D::Result& result) {
-        common::MutexLocker locker(&mutex_);
-        data_.constraints.insert(data_.constraints.end(), result.begin(),
-                                 result.end());
-        notification = true;
-      });
-  locker.Await([&notification]() { return notification; });
+       &notification](const constraints::ConstraintBuilder3D::Result& result)
+          EXCLUDES(mutex_) {
+            common::MutexLocker locker(&mutex_);
+            data_.constraints.insert(data_.constraints.end(), result.begin(),
+                                     result.end());
+            notification = true;
+          });
+  while (!locker.AwaitWithTimeout([&notification]()
+                                      REQUIRES(mutex_) { return notification; },
+                                  common::FromSeconds(1.))) {
+    report_progress();
+  }
+  CHECK_EQ(constraint_builder_.GetNumFinishedNodes(), num_trajectory_nodes);
+  std::cout << "\r\x1b[KOptimizing: Done.     " << std::endl;
 }
 
 void PoseGraph3D::DeleteTrajectory(const int trajectory_id) {
diff --git a/cartographer/mapping/internal/3d/pose_graph_3d.h b/cartographer/mapping/internal/3d/pose_graph_3d.h
index 117c0d5..dc271cc 100644
--- a/cartographer/mapping/internal/3d/pose_graph_3d.h
+++ b/cartographer/mapping/internal/3d/pose_graph_3d.h
@@ -162,7 +162,7 @@ class PoseGraph3D : public PoseGraph {
 
   // Handles a new work item.
   void AddWorkItem(const std::function<WorkItem::Result()>& work_item)
-      EXCLUDES(mutex_);
+      EXCLUDES(mutex_) EXCLUDES(work_queue_mutex_);
 
   // Adds connectivity and sampler for a trajectory if it does not exist.
   void AddTrajectoryIfNeeded(int trajectory_id) REQUIRES(mutex_);
@@ -197,7 +197,7 @@ class PoseGraph3D : public PoseGraph {
 
   // Runs the optimization, executes the trimmers and processes the work queue.
   void HandleWorkQueue(const constraints::ConstraintBuilder3D::Result& result)
-      EXCLUDES(mutex_);
+      EXCLUDES(mutex_) EXCLUDES(work_queue_mutex_);
 
   // Runs the optimization. Callers have to make sure, that there is only one
   // optimization being run at a time.
@@ -229,10 +229,11 @@ class PoseGraph3D : public PoseGraph {
   const proto::PoseGraphOptions options_;
   GlobalSlamOptimizationCallback global_slam_optimization_callback_;
   mutable common::Mutex mutex_;
+  common::Mutex work_queue_mutex_;
 
   // If it exists, further work items must be added to this queue, and will be
   // considered later.
-  std::unique_ptr<WorkQueue> work_queue_ GUARDED_BY(mutex_);
+  std::unique_ptr<WorkQueue> work_queue_ GUARDED_BY(work_queue_mutex_);
 
   // We globally localize a fraction of the nodes from each trajectory.
   std::unordered_map<int, std::unique_ptr<common::FixedRatioSampler>>