diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 82521c8..44247ad 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -220,7 +220,7 @@
     enddef
     defcompile
   END
-  v9.CheckScriptFailure(lines, 'E1089:')
+  v9.CheckScriptFailure(lines, 'E1268:')
 
   g:inc_counter += 1
   assert_equal(2, g:inc_counter)
@@ -2460,6 +2460,49 @@
   g:StopVimInTerminal(buf)
 enddef
 
+def Test_using_s_var_in_function()
+  var lines =<< trim END
+      vim9script
+      var scriptlevel = 123
+      def SomeFunc()
+        echo s:scriptlevel
+      enddef
+      SomeFunc()
+  END
+  v9.CheckScriptFailure(lines, 'E1268:')
+
+  # OK in legacy script
+  lines =<< trim END
+      let s:scriptlevel = 123
+      def s:SomeFunc()
+        echo s:scriptlevel
+      enddef
+      call s:SomeFunc()
+  END
+  v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+      vim9script
+      var scriptlevel = 123
+      def SomeFunc()
+        s:scriptlevel = 456
+      enddef
+      SomeFunc()
+  END
+  v9.CheckScriptFailure(lines, 'E1268:')
+
+  # OK in legacy script
+  lines =<< trim END
+      let s:scriptlevel = 123
+      def s:SomeFunc()
+        s:scriptlevel = 456
+      enddef
+      call s:SomeFunc()
+      call assert_equal(456, s:scriptlevel)
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
 
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/version.c b/src/version.c
index 253cbe8..97a8f6e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4447,
+/**/
     4446,
 /**/
     4445,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 803f19c..6eb6e16 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1331,6 +1331,12 @@
 		    char_u	*rawname = lhs->lhs_name
 					   + (lhs->lhs_name[1] == ':' ? 2 : 0);
 
+		    if (script_namespace && current_script_is_vim9())
+		    {
+			semsg(_(e_cannot_use_s_colon_in_vim9_script_str),
+								    var_start);
+			return FAIL;
+		    }
 		    if (is_decl)
 		    {
 			if (script_namespace)
diff --git a/src/vim9expr.c b/src/vim9expr.c
index 46d14dc..1485bd9 100644
--- a/src/vim9expr.c
+++ b/src/vim9expr.c
@@ -422,8 +422,15 @@
 	    {
 		case 'v': res = generate_LOADV(cctx, name, error);
 			  break;
-		case 's': if (is_expr && ASCII_ISUPPER(*name)
-				       && find_func(name, FALSE) != NULL)
+		case 's': if (current_script_is_vim9())
+			  {
+			      semsg(_(e_cannot_use_s_colon_in_vim9_script_str),
+									 *arg);
+			      vim_free(name);
+			      return FAIL;
+			  }
+			  if (is_expr && ASCII_ISUPPER(*name)
+					     && find_func(name, FALSE) != NULL)
 			      res = generate_funcref(cctx, name, FALSE);
 			  else
 			      res = compile_load_scriptvar(cctx, name,