diff --git a/TODO.md b/TODO.md
index 58b3b0cd..9dc11835 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,6 +1,7 @@
 # features/tweaks
 - emoji picker application
 - find a Masto/Pleroma app which works on mobile
+- remove hardcoded uid/gids outside of allocations.nix (used in impermanence code -- replace with username/groupname)
 
 
 # speed up cross compiling
diff --git a/machines/servo/services/matrix.nix b/machines/servo/services/matrix.nix
index 249090ec..5867a244 100644
--- a/machines/servo/services/matrix.nix
+++ b/machines/servo/services/matrix.nix
@@ -5,6 +5,7 @@
 {
   colinsane.impermanence.service-dirs = [
     # TODO: mode?
+    # user and group are both "matrix-appservice-irc"
     { user = "993"; group = "992"; directory = "/var/lib/matrix-appservice-irc"; }
     { user = "224"; group = "224"; directory = "/var/lib/matrix-synapse"; }
   ];