diff --git a/rules/textproto/less.textproto b/rules/textproto/less.textproto
index 2ccb3de..2aca055 100644
--- a/rules/textproto/less.textproto
+++ b/rules/textproto/less.textproto
@@ -113,7 +113,7 @@ type_rule {
     rule {
       field: "Designation"
       validations {
-        regexp_validate: "^(PE|M2_)\\d+$"
+        regexp_validate: "^((PE|M2_)\\d+|PE\\d_IO[01])$"
       }
     }
     rule {