diff --git a/util/reserved.json b/util/reserved.json
index 757136a13..3cb9d41b4 100644
--- a/util/reserved.json
+++ b/util/reserved.json
@@ -134,6 +134,7 @@
     "tld",
     "token",
     "tokens",
+    "tos",
     "txt",
     "txt[1-9999]",
     "url",