diff --git a/plist-cil/BinaryPropertyListWriter.cs b/plist-cil/BinaryPropertyListWriter.cs
index 77eeab8..b1444d4 100644
--- a/plist-cil/BinaryPropertyListWriter.cs
+++ b/plist-cil/BinaryPropertyListWriter.cs
@@ -24,7 +24,9 @@
 // SOFTWARE.
 using System;
 using System.IO;
+using System.Linq;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 
 namespace Claunia.PropertyList
 {
@@ -162,7 +164,7 @@ namespace Claunia.PropertyList
         long count;
 
         // map from object to its ID
-        Dictionary<NSObject, int> idMap = new Dictionary<NSObject, int>();
+        Collection<NSObject> idMap = new Collection<NSObject>(); //(new IdentityEqualityComparer<NSObject>());
         int idSizeInBytes;
 
         /// <summary>
@@ -220,10 +222,10 @@ namespace Claunia.PropertyList
             long[] offsets = new long[idMap.Count];
 
             // write each object, save offset
-            foreach (KeyValuePair<NSObject, int> entry in idMap)
+            for(int i = 0; i < idMap.Count; i++)
             {
-                NSObject obj = entry.Key;
-                int id = entry.Value;
+                NSObject obj = idMap[i];
+                int id = i;
                 offsets[id] = count;
                 if (obj == null)
                 {
@@ -255,8 +257,7 @@ namespace Claunia.PropertyList
                 // number of objects
                 WriteLong(idMap.Count);
                 // top object
-                int rootID;
-                idMap.TryGetValue(root, out rootID);
+                int rootID = idMap.IndexOf(root);
                 WriteLong(rootID);
                 // offset table offset
                 WriteLong(offsetTableOffset);
@@ -267,17 +268,28 @@ namespace Claunia.PropertyList
 
         internal void AssignID(NSObject obj)
         {
-            if (!idMap.ContainsKey(obj))
+            if(obj is UID)
             {
-                idMap.Add(obj, idMap.Count);
+                idMap.Add(obj);
+            }
+            else if(!idMap.Contains(obj))
+            {
+                idMap.Add(obj);
             }
         }
 
         internal int GetID(NSObject obj)
         {
-            int ID;
-            idMap.TryGetValue(obj, out ID);
-            return ID;
+            if (obj is UID)
+            {
+                var uid = obj as UID;
+                var first = idMap.OfType<UID>().First(v => NSObject.ArrayEquals(v.Bytes, uid.Bytes));
+                return idMap.IndexOf(first);
+            }
+            else
+            {
+                return idMap.IndexOf(obj);
+            }
         }
 
         static int ComputeIdSizeInBytes(int numberOfIds)