diff --git a/modules/misc/ids.nix b/modules/misc/ids.nix
index 0dec1c8b167..ce758f2db7f 100644
--- a/modules/misc/ids.nix
+++ b/modules/misc/ids.nix
@@ -100,7 +100,7 @@
       amule = 90;
       minidlna = 91;
       elasticsearch = 92;
-      tcpcryptd = 666;
+      tcpcryptd = 666; # tcpcryptd hard-codes that UID in its source code. :-(
 
       # When adding a uid, make sure it doesn't match an existing gid.