diff --git a/nixos/modules/services/mail/postfix.nix b/nixos/modules/services/mail/postfix.nix
index fd78c98d0cb4..6bb501959f95 100644
--- a/nixos/modules/services/mail/postfix.nix
+++ b/nixos/modules/services/mail/postfix.nix
@@ -484,7 +484,7 @@ in
       };
 
       config = mkOption {
-        type = with types; attrsOf (oneOf [ bool str (listOf str) ]);
+        type = with types; attrsOf (oneOf [ bool int str (listOf str) ]);
         description = ''
           The main.cf configuration file as key value set.
         '';