diff --git a/Editor/ClusterJson_Drawer.cs b/Editor/ClusterJson_Drawer.cs
index b2a0d8c..dfb61a7 100644
--- a/Editor/ClusterJson_Drawer.cs
+++ b/Editor/ClusterJson_Drawer.cs
@@ -54,14 +54,22 @@ namespace NanoBrain.Unity {
             return EditorGUIUtility.singleLineHeight + propertyExtraHeight;
         }
 
+#if UNITY_6000_0_OR_NEWER
         private readonly Dictionary<EntityId, bool> _invalidCache = new();
+#else
+        private readonly Dictionary<int, bool> _invalidCache = new();
+#endif
 
         private bool IsInvalidJson(SerializedProperty jsonFileProp) {
             TextAsset jsonFile = jsonFileProp.objectReferenceValue as TextAsset;
             if (jsonFile == null)
                 return false;
 
+#if UNITY_6000_0_OR_NEWER
             EntityId id = jsonFile.GetEntityId();
+#else
+            int id = jsonFile.GetInstanceID();
+#endif
             if (_invalidCache.TryGetValue(id, out bool invalid))
                 return invalid;
 
diff --git a/Editor/ClusterView.cs b/Editor/ClusterView.cs
index 214c7f8..beaef17 100644
--- a/Editor/ClusterView.cs
+++ b/Editor/ClusterView.cs
@@ -41,7 +41,7 @@ namespace NanoBrain.Unity {
 #if UNITY_6000_0_OR_NEWER            
             EntityId id = serializedObject.targetObject.GetEntityId();
 #else
-            int id = property.serializedObject.targetObject.GetInstanceID();
+            int id = serializedObject.targetObject.GetInstanceID();
 #endif            
             string key = id.ToString();
             if (!clusterViews.TryGetValue(key, out ClusterView clusterView))