diff --git a/schemas/domain.schema.json b/schemas/domain.schema.json
index d6690de6..0817eaa8 100644
--- a/schemas/domain.schema.json
+++ b/schemas/domain.schema.json
@@ -20,7 +20,7 @@
     },
     "subdomain": {
       "type": "string",
-      "pattern": "^([a-z0-9_*.-]|@)$",
+      "pattern": "^([a-z0-9_*.-]{1,100}|@)$",
       "not": {
         "enum": [
           "a11y",