diff --git a/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs b/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs
index ec02314..70afadb 100644
--- a/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs
+++ b/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs
@@ -150,7 +150,7 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
         (P.DBName "key")
         (P.FTTypeCon Nothing "SessionId sess")
         (P.sqlType (Proxy :: Proxy (SessionId sess)))
-        []
+        ["maxlen=30"]
         True
         P.NoReference
   persistFieldDef PersistentSessionAuthId