diff --git a/Assets/Mirror/Core/SyncDictionary.cs b/Assets/Mirror/Core/SyncDictionary.cs
index 4de1994a9..34be71a59 100644
--- a/Assets/Mirror/Core/SyncDictionary.cs
+++ b/Assets/Mirror/Core/SyncDictionary.cs
@@ -65,12 +65,10 @@ public SyncIDictionary(IDictionary<TKey, TValue> objects)
             this.objects = objects;
         }
 
-        void AddOperation(Operation op, TKey key, TValue item, bool checkAccess)
+        void AddOperation(Operation op, TKey key, TValue item, TValue oldItem, bool checkAccess)
         {
             if (checkAccess && IsReadOnly)
-            {
-                throw new System.InvalidOperationException("SyncDictionaries can only be modified by the owner.");
-            }
+                throw new InvalidOperationException("SyncDictionaries can only be modified by the owner.");
 
             Change change = new Change
             {
@@ -179,15 +177,15 @@ public override void OnDeserializeDelta(NetworkReader reader)
                             // ClientToServer needs to set dirty in server OnDeserialize.
                             // no access check: server OnDeserialize can always
                             // write, even for ClientToServer (for broadcasting).
-                            if (ContainsKey(key))
+                            if (objects.TryGetValue(key, out TValue oldItem))
                             {
-                                objects[key] = item; // assign after ContainsKey check
-                                AddOperation(Operation.OP_SET, key, item, false);
+                                objects[key] = item; // assign after TryGetValue
+                                AddOperation(Operation.OP_SET, key, item, oldItem, false);
                             }
                             else
                             {
-                                objects[key] = item; // assign after ContainsKey check
-                                AddOperation(Operation.OP_ADD, key, item, false);
+                                objects[key] = item; // assign after TryGetValue
+                                AddOperation(Operation.OP_ADD, key, item, default, false);
                             }
                         }
                         break;
@@ -199,7 +197,7 @@ public override void OnDeserializeDelta(NetworkReader reader)
                             // ClientToServer needs to set dirty in server OnDeserialize.
                             // no access check: server OnDeserialize can always
                             // write, even for ClientToServer (for broadcasting).
-                            AddOperation(Operation.OP_CLEAR, default, default, false);
+                            AddOperation(Operation.OP_CLEAR, default, default, default, false);
                             // clear after invoking the callback so users can iterate the dictionary
                             // and take appropriate action on the items before they are wiped.
                             objects.Clear();
@@ -210,14 +208,14 @@ public override void OnDeserializeDelta(NetworkReader reader)
                         key = reader.Read<TKey>();
                         if (apply)
                         {
-                            if (objects.TryGetValue(key, out item))
+                            if (objects.TryGetValue(key, out TValue oldItem))
                             {
                                 // add dirty + changes.
                                 // ClientToServer needs to set dirty in server OnDeserialize.
                                 // no access check: server OnDeserialize can always
                                 // write, even for ClientToServer (for broadcasting).
                                 objects.Remove(key);
-                                AddOperation(Operation.OP_REMOVE, key, item, false);
+                                AddOperation(Operation.OP_REMOVE, key, oldItem, oldItem, false);
                             }
                         }
                         break;
@@ -233,7 +231,7 @@ public override void OnDeserializeDelta(NetworkReader reader)
 
         public void Clear()
         {
-            AddOperation(Operation.OP_CLEAR, default, default, true);
+            AddOperation(Operation.OP_CLEAR, default, default, default, true);
             // clear after invoking the callback so users can iterate the dictionary
             // and take appropriate action on the items before they are wiped.
             objects.Clear();
@@ -243,9 +241,9 @@ public void Clear()
 
         public bool Remove(TKey key)
         {
-            if (objects.TryGetValue(key, out TValue item) && objects.Remove(key))
+            if (objects.TryGetValue(key, out TValue oldItem) && objects.Remove(key))
             {
-                AddOperation(Operation.OP_REMOVE, key, item, true);
+                AddOperation(Operation.OP_REMOVE, key, oldItem, oldItem, true);
                 return true;
             }
             return false;
@@ -258,13 +256,14 @@ public TValue this[TKey i]
             {
                 if (ContainsKey(i))
                 {
+                    TValue oldItem = objects[i];
                     objects[i] = value;
-                    AddOperation(Operation.OP_SET, i, value, true);
+                    AddOperation(Operation.OP_SET, i, value, oldItem, true);
                 }
                 else
                 {
                     objects[i] = value;
-                    AddOperation(Operation.OP_ADD, i, value, true);
+                    AddOperation(Operation.OP_ADD, i, value, default, true);
                 }
             }
         }
@@ -274,7 +273,7 @@ public TValue this[TKey i]
         public void Add(TKey key, TValue value)
         {
             objects.Add(key, value);
-            AddOperation(Operation.OP_ADD, key, value, true);
+            AddOperation(Operation.OP_ADD, key, value, default, true);
         }
 
         public void Add(KeyValuePair<TKey, TValue> item) => Add(item.Key, item.Value);
@@ -301,7 +300,7 @@ public bool Remove(KeyValuePair<TKey, TValue> item)
         {
             bool result = objects.Remove(item.Key);
             if (result)
-                AddOperation(Operation.OP_REMOVE, item.Key, item.Value, true);
+                AddOperation(Operation.OP_REMOVE, item.Key, item.Value, item.Value, true);
 
             return result;
         }