diff --git a/nixos/modules/services/mail/postfix.nix b/nixos/modules/services/mail/postfix.nix
index 47ce2c4c5e3..a3e60cfecad 100644
--- a/nixos/modules/services/mail/postfix.nix
+++ b/nixos/modules/services/mail/postfix.nix
@@ -839,5 +839,8 @@ in
     (mkIf (cfg.extraConfig != "") {
       warnings = [ "The services.postfix.extraConfig option was deprecated. Please use services.postfix.config instead." ];
     })
+    (mkIf (cfg.extraMasterConf != "") {
+      warnings = [ "The services.postfix.extraMasterConf option was deprecated. Please use services.postfix.masterConfig instead." ];
+    })
   ]);
 }