diff --git a/src/evalwindow.c b/src/evalwindow.c
index 98c7ff3..bc59251 100644
--- a/src/evalwindow.c
+++ b/src/evalwindow.c
@@ -889,6 +889,11 @@
     wp = find_win_by_nr_or_id(&argvars[0]);
     if (wp == NULL || win_valid_popup(wp))
 	return;
+    if (!win_valid(wp))
+    {
+	emsg(_(e_cannot_resize_window_in_another_tab_page));
+	return;
+    }
 
     offset = (int)tv_get_number(&argvars[1]);
     win_drag_vsep_line(wp, offset);
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index ce9f932..f8e5a31 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -1652,18 +1652,24 @@
   set laststatus=2
   set mouse=a
   func ClickExpr()
-      call test_setmouse(&lines - 1, 1)
-        return "\<LeftMouse>"
+    call test_setmouse(&lines - 1, 1)
+    return "\<LeftMouse>"
   endfunc
   func DragExpr()
-      call test_setmouse(&lines - 2, 1)
-        return "\<LeftDrag>"
+    call test_setmouse(&lines - 2, 1)
+    return "\<LeftDrag>"
   endfunc
   nnoremap <expr> <F2> ClickExpr()
   nnoremap <expr> <F3> DragExpr()
 
   " this was causing a crash in win_drag_status_line()
   call feedkeys("\<F2>:tabnew\<CR>\<F3>", 'tx')
+
+  nunmap <F2>
+  nunmap <F3>
+  delfunc ClickExpr
+  delfunc DragExpr
+  set laststatus& mouse&
 endfunc
 
 " Test for mapping <LeftDrag> in Insert mode
diff --git a/src/testdir/test_window_cmd.vim b/src/testdir/test_window_cmd.vim
index 8a71913..0d4c278 100644
--- a/src/testdir/test_window_cmd.vim
+++ b/src/testdir/test_window_cmd.vim
@@ -1483,23 +1483,33 @@
   call assert_equal(w0, winwidth(0))
   call assert_true(win_move_separator(0, -1))
   call assert_equal(w0, winwidth(0))
+
   " check that win_move_separator doesn't error with offsets beyond moving
   " possibility
   call assert_true(win_move_separator(id, 5000))
   call assert_true(winwidth(id) > w)
   call assert_true(win_move_separator(id, -5000))
   call assert_true(winwidth(id) < w)
+
   " check that win_move_separator returns false for an invalid window
   wincmd =
   let w = winwidth(0)
   call assert_false(win_move_separator(-1, 1))
   call assert_equal(w, winwidth(0))
+
   " check that win_move_separator returns false for a popup window
   let id = popup_create(['hello', 'world'], {})
   let w = winwidth(id)
   call assert_false(win_move_separator(id, 1))
   call assert_equal(w, winwidth(id))
   call popup_close(id)
+
+  " check that using another tabpage fails without crash
+  let id = win_getid()
+  tabnew
+  call assert_fails('call win_move_separator(id, -1)', 'E1308:')
+  tabclose
+
   %bwipe!
 endfunc
 
diff --git a/src/version.c b/src/version.c
index 16054b0..5d1a2fb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    824,
+/**/
     823,
 /**/
     822,