diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index c673453..48c1cf2 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -1583,6 +1583,7 @@
   assert_equal(true, LambdaUsingArg(1)())
 
   call CheckDefFailure(["filter([1, 2], {k,v -> 1})"], 'E1069:')
+  call CheckDefFailure(["let L = {a -> a + b}"], 'E1001:')
 enddef
 
 def Test_expr7_lambda_vim9script()