diff --git a/src/testdir/test_usercommands.vim b/src/testdir/test_usercommands.vim
index 331e55f..d6ac965 100644
--- a/src/testdir/test_usercommands.vim
+++ b/src/testdir/test_usercommands.vim
@@ -384,6 +384,17 @@
   com! -nargs=? -complete=custom,min DoCmd
   call assert_fails("call feedkeys(':DoCmd \t', 'tx')", 'E118:')
 
+  " custom completion for a pattern with a backslash
+  let g:ArgLead = ''
+  func! CustCompl(A, L, P)
+    let g:ArgLead = a:A
+    return ['one', 'two', 'three']
+  endfunc
+  com! -nargs=? -complete=customlist,CustCompl DoCmd
+  call feedkeys(":DoCmd a\\\t", 'xt')
+  call assert_equal('a\', g:ArgLead)
+  delfunc CustCompl
+
   delcom DoCmd
 endfunc