diff --git a/src/testdir/test_eval_stuff.vim b/src/testdir/test_eval_stuff.vim
index 02e7e14..1490ffb 100644
--- a/src/testdir/test_eval_stuff.vim
+++ b/src/testdir/test_eval_stuff.vim
@@ -135,6 +135,12 @@
   let a = 'a'
   let a..=b
   call assert_equal('ab', a)
+
+  if has('float')
+    let a = 'A'
+    let b = 1.234
+    call assert_fails('echo a .. b', 'E806:')
+  endif
 endfunc
 
 " Test fix for issue #4507