diff --git a/src/window.c b/src/window.c
index eb16e2a433..6da804bbd9 100644
--- a/src/window.c
+++ b/src/window.c
@@ -2668,7 +2668,7 @@ decode_next_window_args (Lisp_Object *window, Lisp_Object *minibuf, Lisp_Object
   XSETWINDOW (*window, w);
   /* MINIBUF nil may or may not include minibuffers.  Decide if it
      does.  */
-  if (NILP (*minibuf))
+  if (WINDOWP (miniwin) & NILP (*minibuf))
     *minibuf = this_minibuffer_depth (XWINDOW (miniwin)->contents)
       ? miniwin
       : Qlambda;
@@ -2682,9 +2682,7 @@ decode_next_window_args (Lisp_Object *window, Lisp_Object *minibuf, Lisp_Object
   /* ALL_FRAMES nil doesn't specify which frames to include.  */
   if (NILP (*all_frames))
     *all_frames
-      = (!EQ (*minibuf, Qlambda)
-	 ? FRAME_MINIBUF_WINDOW (XFRAME (w->frame))
-	 : Qnil);
+      = (WINDOWP (miniwin) && !EQ (*minibuf, Qlambda)) ? miniwin : Qnil;
   else if (EQ (*all_frames, Qvisible))
     ;
   else if (EQ (*all_frames, make_fixnum (0)))