diff --git a/services/prometheus.nix b/services/prometheus.nix
index 0a04a31..2c56280 100644
--- a/services/prometheus.nix
+++ b/services/prometheus.nix
@@ -22,7 +22,7 @@
             targets = lib.pipe config.services.matrix-synapse.settings.listeners [
               (lib.filter (l: l.type == "metrics"))
               builtins.head
-              (l: "[${builtins.head l.bind_addresses}]:${toString l.port}")
+              (l: [ "[${builtins.head l.bind_addresses}]:${toString l.port}" ])
             ];
           }
         ];