diff --git a/OpenSim/Region/Framework/Scenes/Scene.cs b/OpenSim/Region/Framework/Scenes/Scene.cs
index 3576a88b7c..3fc195a5ea 100644
--- a/OpenSim/Region/Framework/Scenes/Scene.cs
+++ b/OpenSim/Region/Framework/Scenes/Scene.cs
@@ -174,6 +174,7 @@ namespace OpenSim.Region.Framework.Scenes
         private bool m_firstHeartbeat = true;
 
         private object m_deleting_scene_object = new object();
+        private object m_cleaningAttachments = new object();
 
         private UpdatePrioritizationSchemes m_priorityScheme = UpdatePrioritizationSchemes.Time;
         private bool m_reprioritizationEnabled = true;
@@ -4995,25 +4996,29 @@ namespace OpenSim.Region.Framework.Scenes
             List<SceneObjectGroup> objectsToDelete =
                     new List<SceneObjectGroup>();
 
-            ForEachSOG(delegate (SceneObjectGroup grp)
-                    {
-                        if (grp.RootPart.Shape.State != 0)
+            lock (m_cleaningAttachments)
+            {
+                ForEachSOG(delegate (SceneObjectGroup grp)
                         {
                             if (grp.RootPart.Shape.PCode == 0 && grp.RootPart.Shape.State != 0 && (!objectsToDelete.Contains(grp)))
                             {
-                                objectsToDelete.Add(grp);
-                                return;
-                            }
+                                UUID agentID = grp.OwnerID;
+                                if (agentID == UUID.Zero)
+                                {
+                                    objectsToDelete.Add(grp);
+                                    return;
+                                }
 
-                            ScenePresence sp = GetScenePresence(agentID);
-                            if (sp == null)
-                            {
-                                objectsToDelete.Add(grp);
-                                return;
+                                ScenePresence sp = GetScenePresence(agentID);
+                                if (sp == null)
+                                {
+                                    objectsToDelete.Add(grp);
+                                    return;
+                                }
                             }
-                        }
-                    });
-            
+                        });
+            }
+
             foreach (SceneObjectGroup grp in objectsToDelete)
             {
                 m_log.InfoFormat("[SCENE]: Deleting dropped attachment {0} of user {1}", grp.UUID, grp.OwnerID);