diff --git a/nixos/modules/services/monitoring/prometheus/exporters/blackbox.nix b/nixos/modules/services/monitoring/prometheus/exporters/blackbox.nix
index 66eaed51d2ea..407bff1d62de 100644
--- a/nixos/modules/services/monitoring/prometheus/exporters/blackbox.nix
+++ b/nixos/modules/services/monitoring/prometheus/exporters/blackbox.nix
@@ -21,7 +21,7 @@ let
       throw
       "${logPrefix}: configuration file must not reside within /tmp - it won't be visible to the systemd service."
     else
-      true;
+      file;
   checkConfig = file:
     pkgs.runCommand "checked-blackbox-exporter.conf" {
       preferLocalBuild = true;