diff --git a/nixos/modules/services/monitoring/prometheus/default.nix b/nixos/modules/services/monitoring/prometheus/default.nix
index 7e707a13b790..4de80acfa9a8 100644
--- a/nixos/modules/services/monitoring/prometheus/default.nix
+++ b/nixos/modules/services/monitoring/prometheus/default.nix
@@ -181,6 +181,10 @@ let
         communicating with external systems (federation, remote
         storage, Alertmanager).
       '';
+
+      query_log_file = mkOpt types.str ''
+        Path to the file prometheus should write its query log to.
+      '';
     };
   };