diff --git a/src/testdir/test_termcodes.vim b/src/testdir/test_termcodes.vim
index 7e450d9..507753c 100644
--- a/src/testdir/test_termcodes.vim
+++ b/src/testdir/test_termcodes.vim
@@ -2256,6 +2256,17 @@
 
   iunmap '
   iunmap <C-W><C-A>
+
+  " clean buffer
+  %d _
+  imap B b
+  imap BBB blimp
+  let input = repeat(GetEscCodeCSI27('B', 2), 3)
+  call feedkeys("a" .. input .. "\<Esc>", 'Lx!')
+  call assert_equal('blimp', getline(1))
+  " cleanup
+  iunmap BBB
+  iunmap B
   set timeoutlen&
 endfunc
 
diff --git a/src/testdir/view_util.vim b/src/testdir/view_util.vim
index 71cb071..161c8b2 100644
--- a/src/testdir/view_util.vim
+++ b/src/testdir/view_util.vim
@@ -71,7 +71,7 @@
 " than the raw code.
 
 " Return the modifyOtherKeys level 2 encoding for "key" with "modifier"
-" (number value, e.g. CTRL is 5).
+" (number value, e.g. CTRL is 5, Shift is 2, Alt is 3).
 func GetEscCodeCSI27(key, modifier)
   let key = printf("%d", char2nr(a:key))
   let mod = printf("%d", a:modifier)