diff --git a/modules/mail/default.nix b/modules/mail/default.nix
index fe90640..1b5718c 100644
--- a/modules/mail/default.nix
+++ b/modules/mail/default.nix
@@ -89,7 +89,7 @@ in
       config = {
         home_mailbox = "Maildir/";
         # 25 MiB
-        message_size_limit = 26214400;
+        message_size_limit = "26214400";
         # hostname used in helo command. It is recommended to have this match the reverse dns entry
         smtp_helo_name = config.networking.rDNS;
         smtp_use_tls = true;