diff --git a/repos/ports/src/virtualbox6/include/fb.h b/repos/ports/src/virtualbox6/include/fb.h
index a4050b346e..bd318721e3 100644
--- a/repos/ports/src/virtualbox6/include/fb.h
+++ b/repos/ports/src/virtualbox6/include/fb.h
@@ -138,11 +138,12 @@ class Genodefb :
 		{
 			HRESULT result = E_FAIL;
 
-			Lock();
 
 			/* save the new bitmap reference */
 			_display->QuerySourceBitmap(screen, _display_bitmap.asOutParam());
 
+			Lock();
+
 			bool const ok = (w <= (ULONG)_gui_win.area.w) &&
 			                (h <= (ULONG)_gui_win.area.h);