diff --git a/interface/src/octree/SafeLanding.cpp b/interface/src/octree/SafeLanding.cpp
index 352c83dad0..ab0ae784f8 100644
--- a/interface/src/octree/SafeLanding.cpp
+++ b/interface/src/octree/SafeLanding.cpp
@@ -35,6 +35,7 @@ void SafeLanding::startEntitySequence(QSharedPointer<EntityTreeRenderer> entityT
         auto entityTree = entityTreeRenderer->getTree();
 
         if (entityTree) {
+            Locker lock(_lock);
             _entityTree = entityTree;
             connect(std::const_pointer_cast<EntityTree>(_entityTree).get(),
                 &EntityTree::addingEntity, this, &SafeLanding::addTrackedEntity);
@@ -47,6 +48,7 @@ void SafeLanding::startEntitySequence(QSharedPointer<EntityTreeRenderer> entityT
 }
 
 void SafeLanding::stopEntitySequence() {
+    Locker lock(_lock);
     _trackingEntities = false;
     _initialStart = INVALID_SEQUENCE;
     _initialEnd = INVALID_SEQUENCE;
@@ -62,10 +64,11 @@ void SafeLanding::addTrackedEntity(const EntityItemID& entityID) {
             const auto& entityType = entity->getType();
             if (entityType == EntityTypes::Model) {
                 ModelEntityItem * modelEntity = std::dynamic_pointer_cast<ModelEntityItem>(entity).get();
-                auto shapeType = modelEntity->getShapeType();
-                if (shapeType == SHAPE_TYPE_COMPOUND || shapeType == SHAPE_TYPE_STATIC_MESH ||
-                    shapeType == SHAPE_TYPE_SIMPLE_COMPOUND) {
+                static const std::set<ShapeType> downloadedCollisionTypes
+                    { SHAPE_TYPE_COMPOUND, SHAPE_TYPE_SIMPLE_COMPOUND, SHAPE_TYPE_STATIC_MESH,  SHAPE_TYPE_SIMPLE_HULL };
+                if (downloadedCollisionTypes.count(modelEntity->getShapeType()) != 0) {
                     // Only track entities with downloaded collision bodies.
+                    Locker lock(_lock);
                     _trackedEntities.emplace(entityID, entity);
                     qCDebug(interfaceapp) << "Safe Landing: Tracking entity " << entity->getItemName();
                 }
@@ -75,27 +78,37 @@ void SafeLanding::addTrackedEntity(const EntityItemID& entityID) {
 }
 
 void SafeLanding::deleteTrackedEntity(const EntityItemID& entityID) {
+    Locker lock(_lock);
     _trackedEntities.erase(entityID);
 }
 
 void SafeLanding::setCompletionSequenceNumbers(int first, int last) {
+    Locker lock(_lock);
     _initialStart = first;
     _initialEnd = (last + 1) % SEQUENCE_MODULO;
-    auto firstIter = _sequenceNumbers.find(_initialStart);
-    if (firstIter != _sequenceNumbers.end()) {
-        _sequenceNumbers.erase(_sequenceNumbers.begin(), firstIter);
-    }
-    _sequenceNumbers.erase(_sequenceNumbers.find(_initialEnd), _sequenceNumbers.end());
 }
 
 void SafeLanding::sequenceNumberReceived(int sequenceNumber) {
     if (_trackingEntities) {
+        Locker lock(_lock);
         _sequenceNumbers.insert(sequenceNumber);
     }
 }
 
+bool SafeLanding::isLoadSequenceComplete() {
+    if (sequenceNumbersComplete() && entityPhysicsComplete()) {
+        Locker lock(_lock);
+        _trackingEntities = false;
+        _trackedEntities.clear();
+        qCDebug(interfaceapp) << "Safe Landing: load sequence complete";
+    }
+
+    return !_trackingEntities;
+}
+
 bool SafeLanding::sequenceNumbersComplete() {
     if (_initialStart != INVALID_SEQUENCE) {
+        Locker lock(_lock);
         auto startIter = _sequenceNumbers.find(_initialStart);
         if (startIter != _sequenceNumbers.end()) {
             _sequenceNumbers.erase(_sequenceNumbers.begin(), startIter);
@@ -109,27 +122,8 @@ bool SafeLanding::sequenceNumbersComplete() {
     return false;
 }
 
-void SafeLanding::resourceLoaded() {
-    QObject * sender = QObject::sender();
-    if (sender) {
-        Resource * resource = dynamic_cast<Resource*>(sender);
-        const QString resourceURL = resource->getURL().toString();
-        _trackedURLs.erase(resourceURL);
-        qCDebug(interfaceapp) << "Safe Landing: Removed tracked URL" << resourceURL;
-    }
-}
-
-bool SafeLanding::isLoadSequenceComplete() {
-    if (sequenceNumbersComplete() && entityPhysicsComplete()) {
-        _trackingEntities = false;
-        _trackedEntities.clear();
-        qCDebug(interfaceapp) << "Safe Landing: load sequence complete";
-    }
-
-    return !_trackingEntities;
-}
-
 bool SafeLanding::entityPhysicsComplete() {
+    Locker lock(_lock);
     for (auto entityMapIter = _trackedEntities.begin(); entityMapIter != _trackedEntities.end(); ++entityMapIter) {
         auto entity = entityMapIter->second;
         if (!entity->shouldBePhysical() || entity->isReadyToComputeShape()) {
diff --git a/interface/src/octree/SafeLanding.h b/interface/src/octree/SafeLanding.h
index e81746e077..a9146f58c7 100644
--- a/interface/src/octree/SafeLanding.h
+++ b/interface/src/octree/SafeLanding.h
@@ -33,13 +33,14 @@ public:
 private slots:
     void addTrackedEntity(const EntityItemID& entityID);
     void deleteTrackedEntity(const EntityItemID& entityID);
-    void resourceLoaded();
 
 private:
     bool sequenceNumbersComplete();
     void debugDumpSequenceIDs() const;
     bool entityPhysicsComplete();
 
+    std::mutex _lock;
+    using Locker = std::lock_guard<std::mutex>;
     bool _trackingEntities { false };
     EntityTreePointer _entityTree;
     using EntityMap = std::map<EntityItemID, EntityItemPointer>;