diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 9ac46f2..11466dc 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -22,6 +22,13 @@
   set whichwrap&
 endfunction
 
+function! Test_isfname()
+  " This used to cause Vim to access uninitialized memory.
+  set isfname=
+  call assert_equal("~X", expand("~X"))
+  set isfname&
+endfunction
+
 function Test_options()
   let caught = 'ok'
   try