diff --git a/src/testdir/test_terminal3.vim b/src/testdir/test_terminal3.vim
index 848e3fa..3cca1b0 100644
--- a/src/testdir/test_terminal3.vim
+++ b/src/testdir/test_terminal3.vim
@@ -10,6 +10,8 @@
 source mouse.vim
 source term_util.vim
 
+import './vim9.vim' as v9
+
 let $PROMPT_COMMAND=''
 
 func Test_terminal_altscreen()
@@ -959,4 +961,18 @@
   call StopVimInTerminal(buf)
 endfunc
 
+" Test for using 'vertical' with term_start(). If a following term_start(),
+" doesn't have the 'vertical' attribute, then it should be split horizontally.
+func Test_terminal_vertical()
+  let lines =<< trim END
+    call term_start("NONE", {'vertical': 1})
+    call term_start("NONE")
+    VAR layout = winlayout()
+    call assert_equal('row', layout[0], string(layout))
+    call assert_equal('col', layout[1][0][0], string(layout))
+    :%bw!
+  END
+  call v9.CheckLegacyAndVim9Success(lines)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab