diff --git a/Facepunch.Steamworks.Test/Client/InventoryTest.cs b/Facepunch.Steamworks.Test/Client/InventoryTest.cs
index 1bcdb8d..837b1b8 100644
--- a/Facepunch.Steamworks.Test/Client/InventoryTest.cs
+++ b/Facepunch.Steamworks.Test/Client/InventoryTest.cs
@@ -15,6 +15,12 @@ public void InventoryDefinitions()
         {
             using ( var client = new Facepunch.Steamworks.Client( 252490 ) )
             {
+               while ( client.Inventory.Definitions == null )
+               {
+                    client.Update();
+                    System.Threading.Thread.Sleep( 10 );
+               }
+
                 Assert.IsNotNull( client.Inventory.Definitions );
                 Assert.AreNotEqual( 0, client.Inventory.Definitions.Length );
 
@@ -36,6 +42,12 @@ public void InventoryDefinitionExchange()
         {
             using ( var client = new Facepunch.Steamworks.Client( 252490 ) )
             {
+                while ( client.Inventory.Definitions == null )
+                {
+                    client.Update();
+                    System.Threading.Thread.Sleep( 10 );
+                }
+
                 Assert.IsNotNull( client.Inventory.Definitions );
                 Assert.AreNotEqual( 0, client.Inventory.Definitions.Length );
 
@@ -58,6 +70,12 @@ public void InventoryDefinitionIngredients()
         {
             using ( var client = new Facepunch.Steamworks.Client( 252490 ) )
             {
+                while ( client.Inventory.Definitions == null )
+                {
+                    client.Update();
+                    System.Threading.Thread.Sleep( 10 );
+                }
+
                 Assert.IsNotNull( client.Inventory.Definitions );
                 Assert.AreNotEqual( 0, client.Inventory.Definitions.Length );
 
@@ -80,6 +98,12 @@ public void InventoryItemList()
         {
             using ( var client = new Facepunch.Steamworks.Client( 252490 ) )
             {
+                while ( client.Inventory.Definitions == null )
+                {
+                    client.Update();
+                    System.Threading.Thread.Sleep( 10 );
+                }
+
                 bool CallbackCalled = false;
 
                 // OnUpdate hsould be called when we receive a list of our items
@@ -146,6 +170,12 @@ public void Deserialize()
         {
             using ( var client = new Facepunch.Steamworks.Client( 252490 ) )
             {
+                while ( client.Inventory.Definitions == null )
+                {
+                    client.Update();
+                    System.Threading.Thread.Sleep( 10 );
+                }
+
                 Assert.IsTrue( client.IsValid );
                 Assert.IsNotNull(client.Inventory.Definitions);
                 Assert.AreNotEqual(0, client.Inventory.Definitions.Length);
@@ -202,6 +232,12 @@ public void PurchaseItems()
         {
             using (var client = new Facepunch.Steamworks.Client(252490))
             {
+                while ( client.Inventory.Definitions == null )
+                {
+                    client.Update();
+                    System.Threading.Thread.Sleep( 10 );
+                }
+
                 Assert.IsNotNull(client.Inventory.Definitions);
                 Assert.AreNotEqual(0, client.Inventory.Definitions.Length);
 
@@ -235,6 +271,12 @@ public void ListPrices()
         {
             using (var client = new Facepunch.Steamworks.Client(252490))
             {
+                while ( client.Inventory.Definitions == null )
+                {
+                    client.Update();
+                    System.Threading.Thread.Sleep( 10 );
+                }
+
                 Assert.IsNotNull(client.Inventory.Definitions);
                 Assert.AreNotEqual(0, client.Inventory.Definitions.Length);
 
diff --git a/Facepunch.Steamworks/BaseSteamworks.cs b/Facepunch.Steamworks/BaseSteamworks.cs
index 9df2019..7d19b7b 100644
--- a/Facepunch.Steamworks/BaseSteamworks.cs
+++ b/Facepunch.Steamworks/BaseSteamworks.cs
@@ -128,8 +128,6 @@ internal void UnregisterCallResult( SteamNative.CallResult handle )
 
         public virtual void Update()
         {
-            Inventory.Update();
-
             Networking.Update();
 
             RunUpdateCallbacks();
@@ -169,6 +167,11 @@ public void UpdateWhile( Func<bool> func )
             }
         }
 
+        /// <summary>
+        /// Debug function, called for every callback. Only really used to confirm that callbacks are working properly.
+        /// </summary>
+        public Action<object> OnAnyCallback;
+
         Dictionary<Type, List<Action<object>>> Callbacks = new Dictionary<Type, List<Action<object>>>();
 
         internal List<Action<object>> CallbackList( Type T )
@@ -192,6 +195,11 @@ internal void OnCallback<T>( T data )
             {
                 i( data );
             }
+
+            if ( OnAnyCallback != null )
+            {
+                OnAnyCallback.Invoke( data );
+            }
         }
 
         internal void RegisterCallback<T>( Action<T> func )
diff --git a/Facepunch.Steamworks/Interfaces/Inventory.cs b/Facepunch.Steamworks/Interfaces/Inventory.cs
index 3953256..bc00919 100644
--- a/Facepunch.Steamworks/Interfaces/Inventory.cs
+++ b/Facepunch.Steamworks/Interfaces/Inventory.cs
@@ -37,24 +37,26 @@ public partial class Inventory : IDisposable
 
         internal SteamNative.SteamInventory inventory;
 
-        private Stopwatch fetchRetryTimer;
-
         private bool IsServer { get; set; }
 
+        public event Action OnDefinitionsUpdated;
+
         internal Inventory( BaseSteamworks steamworks, SteamNative.SteamInventory c, bool server )
         {
             IsServer = server;
             inventory = c;
 
+            steamworks.RegisterCallback<SteamNative.SteamInventoryDefinitionUpdate_t>( onDefinitionsUpdated );
+
             Result.Pending = new Dictionary<int, Result>();
 
-            FetchItemDefinitions();
-            UpdatePrices();
+            FetchItemDefinitions(); // onDefinitionsUpdated should get called on next Update 
 
             if ( !server )
             {
                 steamworks.RegisterCallback<SteamNative.SteamInventoryResultReady_t>( onResultReady );
                 steamworks.RegisterCallback<SteamNative.SteamInventoryFullUpdate_t>( onFullUpdate );
+                
 
                 //
                 // Get a list of our items immediately
@@ -63,6 +65,37 @@ internal Inventory( BaseSteamworks steamworks, SteamNative.SteamInventory c, boo
             }
         }
 
+        /// <summary>
+        /// Should get called when the definitions get updated from Steam.
+        /// </summary>
+        private void onDefinitionsUpdated( SteamInventoryDefinitionUpdate_t obj )
+        {
+            Console.WriteLine( "onDefinitionsUpdated" );
+            LoadDefinitions();
+            UpdatePrices();
+
+            if ( OnDefinitionsUpdated != null )
+            {
+                OnDefinitionsUpdated.Invoke();
+            }
+        }
+
+        private bool LoadDefinitions()
+        {
+            var ids = inventory.GetItemDefinitionIDs();
+            if ( ids == null )
+                return false;
+
+            Definitions = ids.Select( x => CreateDefinition( x ) ).ToArray();
+
+            foreach ( var def in Definitions )
+            {
+                def.Link( Definitions );
+            }
+
+            return true;
+        }
+
         /// <summary>
         /// We've received a FULL update
         /// </summary>
@@ -202,22 +235,7 @@ public Definition CreateDefinition( int id )
         /// </summary>
         public void FetchItemDefinitions()
         {
-            //
-            // Make sure item definitions are loaded, because we're going to be using them.
-            //
-
             inventory.LoadItemDefinitions();
-
-            var ids = inventory.GetItemDefinitionIDs();
-            if ( ids == null )
-                return;
-
-            Definitions = ids.Select( x => CreateDefinition( x ) ).ToArray();
-
-            foreach ( var def in Definitions )
-            {
-                def.Link( Definitions );
-            }
         }
 
         /// <summary>
@@ -225,24 +243,7 @@ public void FetchItemDefinitions()
         /// </summary>
         public void Update()
         {
-            if ( Definitions == null )
-            {
-                //
-                // Don't try every frame, just try every 10 seconds.
-                //
-                {
-                    if ( fetchRetryTimer != null && fetchRetryTimer.Elapsed.TotalSeconds < 10.0f )
-                        return;
 
-                    if ( fetchRetryTimer == null )
-                        fetchRetryTimer = Stopwatch.StartNew();
-
-                    fetchRetryTimer.Reset();
-                    fetchRetryTimer.Start();
-                }
-
-                FetchItemDefinitions();
-            }
         }
 
         /// <summary>
@@ -258,7 +259,10 @@ public IEnumerable<Definition> DefinitionsWithPrices
         {
             get
             {
-                for( int i=0; i< Definitions.Length; i++ )
+                if ( Definitions == null )
+                    yield break;
+
+                for ( int i=0; i< Definitions.Length; i++ )
                 {
                     if (Definitions[i].LocalPrice > 0)
                         yield return Definitions[i];