diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index c0b4259..9a4b597 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -1621,6 +1621,7 @@
   call assert_fails('eval trim("  vim  ", " ", [])', 'E745:')
   call assert_fails('eval trim("  vim  ", " ", -1)', 'E475:')
   call assert_fails('eval trim("  vim  ", " ", 3)', 'E475:')
+  call assert_fails('eval trim("  vim  ", 0)', 'E475:')
 
   let chars = join(map(range(1, 0x20) + [0xa0], {n -> n->nr2char()}), '')
   call assert_equal("x", trim(chars . "x" . chars))