diff --git a/ci.nix b/ci.nix
index 2cc8b66e..bb9b5232 100644
--- a/ci.nix
+++ b/ci.nix
@@ -24,6 +24,7 @@ in
       xo-testutil
       xo-alloc2
       xo-refcnt
+      xo-pyutil
       xo-reflect
       xo-stringtable2
       xo-object2