diff --git a/nixos/modules/services/monitoring/grafana.nix b/nixos/modules/services/monitoring/grafana.nix
index 4ebde6f9b107..1dd740014fa8 100644
--- a/nixos/modules/services/monitoring/grafana.nix
+++ b/nixos/modules/services/monitoring/grafana.nix
@@ -337,11 +337,16 @@ in {
       defaultText = "pkgs.grafana";
       type = types.package;
     };
+
     declarativePlugins = mkOption {
       type = with types; nullOr (listOf path);
       default = null;
       description = "If non-null, then a list of packages containing Grafana plugins to install. If set, plugins cannot be manually installed.";
       example = literalExample "with pkgs.grafanaPlugins; [ grafana-piechart-panel ]";
+      # Make sure each plugin is added only once; otherwise building
+      # the link farm fails, since the same path is added multiple
+      # times.
+      apply = x: if isList x then lib.unique x else x;
     };
 
     dataDir = mkOption {