diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 6db2718..51a6c6f 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -311,6 +311,8 @@
 
   for name in ['true',
                'false',
+               'this',
+               'super',
                'null',
                'null_blob',
                'null_dict',
@@ -322,6 +324,15 @@
     v9.CheckDefExecAndScriptFailure(['var ' .. name .. ' =  0'], 'E1034:')
     v9.CheckDefExecAndScriptFailure(['var ' .. name .. ': bool'], 'E1034:')
   endfor
+
+  var lines =<< trim END
+      vim9script
+      def Foo(super: bool)
+	echo 'something'
+      enddef
+      defcompile
+  END
+  v9.CheckScriptFailure(lines, 'E1034:')
 enddef
 
 def Test_null_values()
@@ -1526,6 +1537,7 @@
   v9.CheckDefFailure(['var false = 1'], 'E1034:')
   v9.CheckDefFailure(['var null = 1'], 'E1034:')
   v9.CheckDefFailure(['var this = 1'], 'E1034:')
+  v9.CheckDefFailure(['var super = 1'], 'E1034:')
 
   v9.CheckDefFailure(['[a; b; c] = g:list'], 'E1001:')
   v9.CheckDefFailure(['var [a; b; c] = g:list'], 'E1080:')
diff --git a/src/userfunc.c b/src/userfunc.c
index 1275884..47c3161 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -86,12 +86,23 @@
 	return arg;
     }
 
-    // Vim9 script: cannot use script var name for argument. In function: also
-    // check local vars and arguments.
-    if (!skip && argtypes != NULL && check_defined(arg, p - arg,
-			       evalarg == NULL ? NULL : evalarg->eval_cctx,
+    // Extra checks in Vim9 script.
+    if (!skip && argtypes != NULL)
+    {
+	int c = *p;
+	*p = NUL;
+	int r = check_reserved_name(arg, FALSE);
+	*p = c;
+	if (r == FAIL)
+	    return arg;
+
+	// Cannot use script var name for argument. In function: also check
+	// local vars and arguments.
+	if (check_defined(arg, p - arg,
+				   evalarg == NULL ? NULL : evalarg->eval_cctx,
 			       eap == NULL ? NULL : eap->cstack, TRUE) == FAIL)
-	return arg;
+	    return arg;
+    }
 
     if (newargs != NULL && ga_grow(newargs, 1) == FAIL)
 	return arg;
diff --git a/src/version.c b/src/version.c
index e8ff7e7..fa900c1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1625,
+/**/
     1624,
 /**/
     1623,
diff --git a/src/vim9script.c b/src/vim9script.c
index b1849db..a64ce72 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -1122,6 +1122,7 @@
     "null_string",
     "null_channel",
     "null_job",
+    "super",
     "this",
     NULL
 };