diff --git a/tasks/setup-Debian.yml b/tasks/setup-Debian.yml
index ae7187d..f286052 100644
--- a/tasks/setup-Debian.yml
+++ b/tasks/setup-Debian.yml
@@ -43,4 +43,5 @@
   template:
     src: apt-preferences-docker.j2
     dest: /etc/apt/preferences.d/docker
-  when: docker_apt_version | length > 0
+  when: docker_apt_version is defined and
+        docker_apt_version | length > 0