3 files changed, 24 insertions, 4 deletions
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 79c93f1917..e676e2e656 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -9690,6 +9690,10 @@ static void f_win_move_separator(typval_T *argvars, typval_T *rettv, EvalFuncDat
   if (wp == NULL || wp->w_floating) {
     return;
   }
+  if (!win_valid(wp)) {
+    emsg(_(e_cannot_resize_window_in_another_tab_page));
+    return;
+  }
 
   int offset = (int)tv_get_number(&argvars[1]);
   win_drag_vsep_line(wp, offset);
diff --git a/src/nvim/testdir/test_mapping.vim b/src/nvim/testdir/test_mapping.vim
index a286774d56..560883ba5d 100644
--- a/src/nvim/testdir/test_mapping.vim
+++ b/src/nvim/testdir/test_mapping.vim
@@ -1054,18 +1054,24 @@ func Test_mouse_drag_statusline()
   set laststatus=2
   set mouse=a
   func ClickExpr()
-      call Ntest_setmouse(&lines - 1, 1)
-        return "\<LeftMouse>"
+    call Ntest_setmouse(&lines - 1, 1)
+    return "\<LeftMouse>"
   endfunc
   func DragExpr()
-      call Ntest_setmouse(&lines - 2, 1)
-        return "\<LeftDrag>"
+    call Ntest_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/nvim/testdir/test_window_cmd.vim b/src/nvim/testdir/test_window_cmd.vim
index 902a3791d4..f38eaaf318 100644
--- a/src/nvim/testdir/test_window_cmd.vim
+++ b/src/nvim/testdir/test_window_cmd.vim
@@ -1393,17 +1393,20 @@ func Test_win_move_separator()
   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 floating window
   let id = nvim_open_win(
         \ 0, 0, #{relative: 'editor', row: 2, col: 2, width: 5, height: 3})
@@ -1411,6 +1414,13 @@ func Test_win_move_separator()
   call assert_false(win_move_separator(id, 1))
   call assert_equal(w, winwidth(id))
   call nvim_win_close(id, 1)
+
+  " 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