diff --git a/OpenSim/Region/CoreModules/World/Access/AccessModule.cs b/OpenSim/Region/CoreModules/World/Access/AccessModule.cs
index 1599f1537f..f567cab8bf 100644
--- a/OpenSim/Region/CoreModules/World/Access/AccessModule.cs
+++ b/OpenSim/Region/CoreModules/World/Access/AccessModule.cs
@@ -91,13 +91,17 @@ namespace OpenSim.Region.CoreModules.World
 
         public void AddRegion(Scene scene)
         {
-            if (!m_SceneList.Contains(scene))
-                m_SceneList.Add(scene);
+            lock (m_SceneList)
+            {
+                if (!m_SceneList.Contains(scene))
+                    m_SceneList.Add(scene);
+            }
         }
 
         public void RemoveRegion(Scene scene)
         {
-            m_SceneList.Remove(scene);
+            lock (m_SceneList)
+                m_SceneList.Remove(scene);
         }
 
         public void RegionLoaded(Scene scene)