diff --git a/src/evalfunc.c b/src/evalfunc.c
index e02b757..cea002f 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -603,7 +603,6 @@
 {
     if (type->tt_type == VAR_STRING
 	    || type->tt_type == VAR_PARTIAL
-	    || type->tt_type == VAR_NUMBER  // 1 means ignore case
 	    || type == &t_unknown
 	    || type == &t_any)
 	return OK;
diff --git a/src/list.c b/src/list.c
index 578d6f1..88f3102 100644
--- a/src/list.c
+++ b/src/list.c
@@ -2198,7 +2198,8 @@
     if (in_vim9script()
 	    && (check_for_list_arg(argvars, 0) == FAIL
 		|| (argvars[1].v_type != VAR_UNKNOWN
-		    && check_for_opt_dict_arg(argvars, 2) == FAIL)))
+		    && (check_for_string_or_func_arg(argvars, 1) == FAIL
+			      || check_for_opt_dict_arg(argvars, 2) == FAIL))))
 	return;
 
     if (argvars[0].v_type != VAR_LIST)
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 5337254..89b7f04 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -949,7 +949,7 @@
         call assert_equal([-1, 'one', 'two', 'three', 'four', 1.0e-15, 0.22, 7, 9, 12, 18, 22, 255], sort(copy(l), 'n'))
 
         LET l = [7, 9, 18, 12, 22, 10.0e-16, -1, 0xff, 0, -0, 0.22, 'bar', 'BAR', 'Bar', 'Foo', 'FOO', 'foo', 'FOOBAR', {}, []]
-        call assert_equal(['bar', 'BAR', 'Bar', 'Foo', 'FOO', 'foo', 'FOOBAR', -1, 0, 0, 0.22, 1.0e-15, 12, 18, 22, 255, 7, 9, [], {}], sort(copy(l), 1))
+        call assert_equal(['bar', 'BAR', 'Bar', 'Foo', 'FOO', 'foo', 'FOOBAR', -1, 0, 0, 0.22, 1.0e-15, 12, 18, 22, 255, 7, 9, [], {}], sort(copy(l), 'i'))
         call assert_equal(['bar', 'BAR', 'Bar', 'Foo', 'FOO', 'foo', 'FOOBAR', -1, 0, 0, 0.22, 1.0e-15, 12, 18, 22, 255, 7, 9, [], {}], sort(copy(l), 'i'))
         call assert_equal(['BAR', 'Bar', 'FOO', 'FOOBAR', 'Foo', 'bar', 'foo', -1, 0, 0, 0.22, 1.0e-15, 12, 18, 22, 255, 7, 9, [], {}], sort(copy(l)))
       endif
@@ -961,6 +961,16 @@
   call assert_fails("call sort([1, 2], function('min'), 1)", "E715:")
   call assert_fails("call sort([1, 2], function('invalid_func'))", "E700:")
   call assert_fails("call sort([1, 2], function('min'))", "E118:")
+
+  let lines =<< trim END
+    call sort(['a', 'b'], 0)
+  END
+  call v9.CheckDefAndScriptFailure(lines, 'E1256: String or function required for argument 2')
+
+  let lines =<< trim END
+    call sort(['a', 'b'], 1)
+  END
+  call v9.CheckDefAndScriptFailure(lines, 'E1256: String or function required for argument 2')
 endfunc
 
 " reduce a list, blob or string
diff --git a/src/version.c b/src/version.c
index 5da1833..b5d93fb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4455,
+/**/
     4454,
 /**/
     4453,