From 841df47fd14d610caed6555cd4be0e0f951d74a8 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Thu, 10 May 2018 13:43:29 +0100
Subject: [PATCH] minor fix.

---
 src/Windows/Avalonia.Win32/WindowImpl.cs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/Windows/Avalonia.Win32/WindowImpl.cs b/src/Windows/Avalonia.Win32/WindowImpl.cs
index 92913ef9eb..bfe4b69eef 100644
--- a/src/Windows/Avalonia.Win32/WindowImpl.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.cs
@@ -29,6 +29,7 @@ namespace Avalonia.Win32
         private string _className;
         private IntPtr _hwnd;
         private IInputRoot _owner;
+        private IntPtr _ownerHandle;
         private bool _trackingMouse;
         private bool _decorated = true;
         private bool _resizable = true;
@@ -876,7 +877,14 @@ namespace Avalonia.Win32
 
         public void SetOwner(IWindowImpl owner)
         {
-            UnmanagedMethods.SetWindowLong(_hwnd, -8, (uint)owner.Handle.Handle);
+            if(_ownerHandle == IntPtr.Zero && owner.Handle.Handle == IntPtr.Zero)
+            {
+                return; // this would cause a failure Error 1400.
+            }
+
+            UnmanagedMethods.SetWindowLong(_hwnd, (int)WindowLongParam.GWL_HWNDPARENT, (uint)owner.Handle.Handle);
+
+            _ownerHandle = owner.Handle.Handle;
         }
     }
 }