diff --git a/src/evalfunc.c b/src/evalfunc.c
index e8ed4ba..1b93200 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -624,6 +624,8 @@
 	    where_T where = WHERE_INIT;
 
 	    args[1] = args[0];
+	    if (type->tt_argcount == -1)
+		t_func_exp.tt_argcount = -1;
 	    where.wt_index = 2;
 	    return check_type(&t_func_exp, type, TRUE, where);
 	}
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index dfec991..7577aec 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -3812,6 +3812,17 @@
       sort([1, 2, 3], (a: any, b: any) => 1)
   END
   v9.CheckDefAndScriptSuccess(lines)
+
+  lines =<< trim END
+      vim9script
+      def SortedList(): list<number>
+        var Lambda: func: number = (a, b): number => a - b
+        var l = [3, 2, 1]
+        return l->sort(Lambda)
+      enddef
+      SortedList()->assert_equal([1, 2, 3])
+  END
+  v9.CheckScriptSuccess(lines)
 enddef
 
 def Test_sort_compare_func_fails()
diff --git a/src/version.c b/src/version.c
index 800925d..f8fb313 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4459,
+/**/
     4458,
 /**/
     4457,