diff --git a/nixos/modules/services/monitoring/prometheus/default.nix b/nixos/modules/services/monitoring/prometheus/default.nix
index d692dd5fc79..a07445ce167 100644
--- a/nixos/modules/services/monitoring/prometheus/default.nix
+++ b/nixos/modules/services/monitoring/prometheus/default.nix
@@ -191,6 +191,7 @@ let
       };
       labels = mkOption {
         type = types.attrsOf types.str;
+        default = {};
         description = ''
           Labels assigned to all metrics scraped from the targets.
         '';