diff --git a/nixos/modules/services/mail/opensmtpd.nix b/nixos/modules/services/mail/opensmtpd.nix
index fb94560e10a..2de7ef48ad1 100644
--- a/nixos/modules/services/mail/opensmtpd.nix
+++ b/nixos/modules/services/mail/opensmtpd.nix
@@ -48,12 +48,12 @@ in {
       };
 
       serverConfiguration = mkOption {
-        type = types.string;
+        type = types.lines;
         default = "";
         example = ''
           listen on lo
           accept for any deliver to lmtp localhost:24
-        ''; 
+        '';
         description = ''
           The contents of the smtpd.conf configuration file. See the
           OpenSMTPD documentation for syntax information. If this option