diff --git a/src/evalfunc.c b/src/evalfunc.c
index 69b4a23..cea002f 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -596,6 +596,43 @@
 }
 
 /*
+ * Check second argument of sort() and uniq(), the "how" argument.
+ */
+    static int
+arg_sort_how(type_T *type, type_T *decl_type UNUSED, argcontext_T *context)
+{
+    if (type->tt_type == VAR_STRING
+	    || type->tt_type == VAR_PARTIAL
+	    || type == &t_unknown
+	    || type == &t_any)
+	return OK;
+
+    if (type->tt_type == VAR_FUNC)
+    {
+	type_T *(args[2]);
+	type_T t_func_exp = {VAR_FUNC, 2, 0, 0, &t_number, args};
+
+	if (context->arg_types[0].type_curr->tt_type == VAR_LIST)
+	    args[0] = context->arg_types[0].type_curr->tt_member;
+	else
+	    args[0] = &t_unknown;
+	if ((type->tt_member != &t_any && type->tt_member != &t_unknown)
+		|| args[0] != &t_unknown)
+	{
+	    where_T where = WHERE_INIT;
+
+	    args[1] = args[0];
+	    where.wt_index = 2;
+	    return check_type(&t_func_exp, type, TRUE, where);
+	}
+
+	return OK;
+    }
+    semsg(_(e_string_or_function_required_for_argument_nr), 2);
+    return FAIL;
+}
+
+/*
  * Check an expression argument, can be a string, funcref or partial.
  * Also accept a bool, a constant resulting from compiling a string argument.
  * Also accept a number, one and zero are accepted.
@@ -1006,7 +1043,7 @@
 static argcheck_T arg02_sign_getplaced[] = {arg_buffer, arg_dict_any};
 static argcheck_T arg45_sign_place[] = {arg_number, arg_string, arg_string, arg_buffer, arg_dict_any};
 static argcheck_T arg23_slice[] = {arg_slice1, arg_number, arg_number};
-static argcheck_T arg13_sortuniq[] = {arg_list_any, NULL, arg_dict_any};
+static argcheck_T arg13_sortuniq[] = {arg_list_any, arg_sort_how, arg_dict_any};
 static argcheck_T arg24_strpart[] = {arg_string, arg_number, arg_number, arg_bool};
 static argcheck_T arg12_system[] = {arg_string, arg_str_or_nr_or_list};
 static argcheck_T arg23_win_execute[] = {arg_number, arg_string_or_list_string, arg_string};
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 2c183fd..7366b8c 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -3796,19 +3796,41 @@
     assert_equal([1, 2, 3, 4, 5, 6, 7, 8], l)
   END
   v9.CheckDefAndScriptSuccess(lines)
-  v9.CheckDefAndScriptFailure(['sort("a")'], ['E1013: Argument 1: type mismatch, expected list<any> but got string', 'E1211: List required for argument 1'])
-  v9.CheckDefAndScriptFailure(['sort([1], "", [1])'], ['E1013: Argument 3: type mismatch, expected dict<any> but got list<number>', 'E1206: Dictionary required for argument 3'])
+
+  lines =<< trim END
+      sort([1, 2, 3], (a: any, b: any) => 1)
+  END
+  v9.CheckDefAndScriptSuccess(lines)
 enddef
 
 def Test_sort_compare_func_fails()
+  v9.CheckDefAndScriptFailure(['sort("a")'], ['E1013: Argument 1: type mismatch, expected list<any> but got string', 'E1211: List required for argument 1'])
+  v9.CheckDefAndScriptFailure(['sort([1], "", [1])'], ['E1013: Argument 3: type mismatch, expected dict<any> but got list<number>', 'E1206: Dictionary required for argument 3'])
+
   var lines =<< trim END
     vim9script
     echo ['a', 'b', 'c']->sort((a: number, b: number) => 0)
   END
   writefile(lines, 'Xbadsort')
   assert_fails('source Xbadsort', ['E1013:', 'E702:'])
-
   delete('Xbadsort')
+
+  lines =<< trim END
+      var l = [1, 2, 3]
+      sort(l, (a: string, b: number) => 1)
+  END
+  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(?number, ?number): number but got func(string, number): number', 'E1013: Argument 1: type mismatch, expected string but got number'])
+
+  lines =<< trim END
+      var l = ['a', 'b', 'c']
+      sort(l, (a: string, b: number) => 1)
+  END
+  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(?string, ?string): number but got func(string, number): number', 'E1013: Argument 2: type mismatch, expected number but got string'])
+
+  lines =<< trim END
+      sort([1, 2, 3], (a: number, b: number) => true)
+  END
+  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(?number, ?number): number but got func(number, number): bool', 'E1138: Using a Bool as a Number'])
 enddef
 
 def Test_spellbadword()
diff --git a/src/version.c b/src/version.c
index 1c99de5..2cc4155 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4449,
+/**/
     4448,
 /**/
     4447,