diff --git a/nixos/modules/services/monitoring/prometheus/alertmanager.nix b/nixos/modules/services/monitoring/prometheus/alertmanager.nix
index 43b4a41eaf33..7d790b6b590b 100644
--- a/nixos/modules/services/monitoring/prometheus/alertmanager.nix
+++ b/nixos/modules/services/monitoring/prometheus/alertmanager.nix
@@ -106,7 +106,8 @@ in {
         type = types.str;
         default = "";
         description = ''
-          Address to listen on for the web interface and API.
+          Address to listen on for the web interface and API. Empty string will listen on all interfaces.
+          "localhost" will listen on 127.0.0.1 (but not ::1).
         '';
       };