diff --git a/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs b/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs
index c88158a6..53ce4d98 100644
--- a/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs
+++ b/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs
@@ -334,6 +334,7 @@ internal void AttachDrag(bool onActivated = true)
 			}
 			else
 			{
+				CaptureMouse();
 				var windowHandle = new WindowInteropHelper(this).Handle;
 				var lParam = new IntPtr(((int)Left & 0xFFFF) | ((int)Top << 16));
 				Win32Helper.SendMessage(windowHandle, Win32Helper.WM_NCLBUTTONDOWN, new IntPtr(Win32Helper.HT_CAPTION), lParam);