diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 68210b2bcaf7238d551d428e6b7e5c6c3e62ee43..6b6eabbd13d78766a520eba52ad06b2ca2af9b45 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -36,6 +36,7 @@ build-coq.8.12.0:
   <<: *template
   variables:
     OPAM_PINS: "coq version 8.12.0"
+    DENY_WARNINGS: "1"
 
 build-coq.8.11.2:
   <<: *template