diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index cedd587c5..03c7f9786 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -54,7 +54,7 @@ build:
         - meson mutter mutter/build --prefix=/usr -Dtests=false
         - ninja -C mutter/build install
     script:
-        - meson . build -Dbuiltype=debugoptimized -Dman=false
+        - meson . build -Dbuiltype=debugoptimized -Dman=false --werror
         - ninja -C build
         - ninja -C build install
     <<: *only_default