diff --git a/libraries/entities/src/EntitySimulation.h b/libraries/entities/src/EntitySimulation.h
index 7d244086e5..0aad55b268 100644
--- a/libraries/entities/src/EntitySimulation.h
+++ b/libraries/entities/src/EntitySimulation.h
@@ -57,10 +57,10 @@ public:
 
     friend class EntityTree;
 
-    virtual void addAction(EntityActionPointer action) { _actionsToAdd += action; }
-    virtual void removeAction(const QUuid actionID) { _actionsToRemove += actionID; }
-    virtual void removeActions(QList<QUuid> actionIDsToRemove) { _actionsToRemove += actionIDsToRemove; }
-    virtual void applyActionChanges() { _actionsToAdd.clear(); _actionsToRemove.clear(); }
+    virtual void addAction(EntityActionPointer action) { lock(); _actionsToAdd += action; unlock(); }
+    virtual void removeAction(const QUuid actionID) { lock(); _actionsToRemove += actionID; unlock(); }
+    virtual void removeActions(QList<QUuid> actionIDsToRemove) { lock(); _actionsToRemove += actionIDsToRemove; unlock(); }
+    virtual void applyActionChanges() { lock(); _actionsToAdd.clear(); _actionsToRemove.clear(); unlock(); }
 
 protected: // these only called by the EntityTree?
     /// \param entity pointer to EntityItem to be added
diff --git a/libraries/physics/src/PhysicalEntitySimulation.cpp b/libraries/physics/src/PhysicalEntitySimulation.cpp
index c68b993fe2..506e5fb67e 100644
--- a/libraries/physics/src/PhysicalEntitySimulation.cpp
+++ b/libraries/physics/src/PhysicalEntitySimulation.cpp
@@ -237,12 +237,15 @@ void PhysicalEntitySimulation::handleCollisionEvents(CollisionEvents& collisionE
 
 void PhysicalEntitySimulation::applyActionChanges() {
     if (_physicsEngine) {
+        lock();
         foreach (EntityActionPointer actionToAdd, _actionsToAdd) {
             _physicsEngine->addAction(actionToAdd);
         }
+        _actionsToAdd.clear();
         foreach (QUuid actionToRemove, _actionsToRemove) {
             _physicsEngine->removeAction(actionToRemove);
         }
+        _actionsToRemove.clear();
+        unlock();
     }
-    EntitySimulation::applyActionChanges();
 }