To reproduce: Use the approach here: http://docs.telerik.com/devtools/winforms/dock/object-model/customizing-floating-windows Workaround: private void RadDock1_FloatingWindowCreated(object sender, Telerik.WinControls.UI.Docking.FloatingWindowEventArgs e) { e.Window = new MyWindow(radDock1); e.Window.FormBorderStyle = System.Windows.Forms.FormBorderStyle.Sizable; } class MyWindow : FloatingWindow { public MyWindow(RadDock dock): base(dock) { } protected override CreateParams CreateParams { get { CreateParams cp = base.CreateParams; cp.Style |= NativeMethods.WS_THICKFRAME; return cp; } } }