diff --git a/nixos/modules/monitoring/server/prometheus.nix b/nixos/modules/monitoring/server/prometheus.nix
index 2a78dd3e797c0b28d14fc9e9e0858811ac86ef76..fac29c29ffaae507549f78826edd3e838ccb4e6c 100644
--- a/nixos/modules/monitoring/server/prometheus.nix
+++ b/nixos/modules/monitoring/server/prometheus.nix
@@ -13,6 +13,7 @@ let
     regex = "^(.*)(?:\\.monitoringvpn):\\d+$";
     target_label = "instance";
   };
+  logRetention = toString(config.services.private-storage.monitoring.policy.logRetentionSeconds) + "s";
 
 in {
   options.services.private-storage.monitoring.prometheus = {
@@ -44,6 +45,7 @@ in {
     services.prometheus = {
       enable = true;
       # port = 9090; # Option only in recent (20.09?) nixpkgs, 9090 default
+      retentionTime = logRetention;
       scrapeConfigs = [
         {
           job_name = "node-exporters";