diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 558f23c..6f9aa0c 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -128,6 +128,7 @@
   assert_equal('one,foo', MyDefVarargs('one'))
   assert_equal('one,two', MyDefVarargs('one', 'two'))
   assert_equal('one,two,three', MyDefVarargs('one', 'two', 'three'))
+  call CheckDefFailure(['MyDefVarargs("one", 22)'], 'E1013: argument 2: type mismatch, expected string but got number')
 enddef
 
 " Only varargs