diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 23af532..3164ca2 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -2169,6 +2169,8 @@
   call assert_equal(1, charclass('.'))
   call assert_equal(2, charclass('x'))
   call assert_equal(3, charclass("\u203c"))
+  " this used to crash vim
+  call assert_equal(0, "xxx"[-1]->charclass())
 endfunc
 
 func Test_eventhandler()