diff --git a/etc/xo/subsystem-list b/etc/xo/subsystem-list
index 6568ccbc..eea49525 100644
--- a/etc/xo/subsystem-list
+++ b/etc/xo/subsystem-list
@@ -20,6 +20,7 @@ xo-type
 xo-procedure2
 xo-numeric
 xo-tokenizer2
+xo-expression2
 xo-allocutil
 xo-alloc
 xo-object