diff --git a/pkgs/uvms-guest/guest.py b/pkgs/uvms-guest/guest.py
index 575245e..04914a9 100644
--- a/pkgs/uvms-guest/guest.py
+++ b/pkgs/uvms-guest/guest.py
@@ -68,7 +68,7 @@ class Processes:
         con, (cid, port) = serv.accept()
         assert cid == 2, cid
         self.sources.append(con)
-        self.client_fds.insert(con.fileno())
+        self.client_fds.add(con.fileno())
         return con, (cid, port)