diff --git a/_CoqProject b/_CoqProject
index aef49c4c82ae2fbeb79634b165c72ef5f30dc676..2015a40abf66dcbb6c7ce88253144d6abec5d8f8 100644
--- a/_CoqProject
+++ b/_CoqProject
@@ -7,6 +7,8 @@
 # Custom flags (to be kept in sync with the dune file at the root of the repo).
 # Fixing this one requires Coq 8.19
 -arg -w -arg -argument-scope-delimiter
+# Fixing this requires Coq 8.20.
+-arg -w -arg -deprecated-since-8.20
 
 stdpp/options.v
 stdpp/base.v