diff --git a/tests/ci-install.sh b/tests/ci-install.sh
index 8111809f..326ab35b 100755
--- a/tests/ci-install.sh
+++ b/tests/ci-install.sh
@@ -4,6 +4,7 @@ set -euo pipefail
 set -x
 
 NULL=
+: "${ci_distro:=debian}"
 : "${ci_docker:=}"
 : "${ci_in_docker:=no}"
 : "${ci_suite:=jessie}"