diff --git a/.cirrus.yml b/.cirrus.yml
index c144e75b7..9d80ea07d 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -141,7 +141,7 @@ rocky_task:
     LC_ALL: C
     CIRRUS_CLONE_DEPTH: 1
     USE_CONFIG: yes
-    CFLAGS: -std=gnu90
+    CFLAGS: -std=gnu90 -Wformat -Wformat=2
 
   # NB: we could consider building a docker image with these
   # preinstalled and specifying that instead, to speed up testing.