diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8e9cb4d600d8a7c7060c89c4377112e5604d8f9e..16a68d773bcef35abc592e3bdba0a9faa2e1df6a 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -38,6 +38,7 @@ build-coq.8.12.0:
   <<: *template
   variables:
     OPAM_PINS: "coq version 8.12.0"
+    DENY_WARNINGS: "1"
 
 build-coq.8.11.2:
   <<: *template