diff --git a/roles/prometheus/tasks/blackbox.yml b/roles/prometheus/tasks/blackbox.yml
index adb4bad..6c29004 100644
--- a/roles/prometheus/tasks/blackbox.yml
+++ b/roles/prometheus/tasks/blackbox.yml
@@ -2,12 +2,12 @@
 
 - name: initialize list of blackbox modules
   set_fact:
-    _blackbox_modules: []
+    _blackbox_modules: {}
 
 - name: build list of blackbox modules
   set_fact:
-    _blackbox_modules: "{{ _blackbox_modules.update(item) }}"
-  loop: "{{ hostvars[inventory_hostname] | dict2items | selectattr('key', 'match', '^prometheus_job_.+$') | map(attribute='value') | map(attribute='blackbox') | map(attribute='modules') | filter('present') | dict }}"
+    _blackbox_modules: "{% set _ = _blackbox_modules.update(item) %}{{ _blackbox_modules }}"
+  loop: "{{ hostvars[inventory_hostname] | dict2items | selectattr('key', 'match', '^prometheus_job_.+$') | map(attribute='value') | map(attribute='blackbox') | map(attribute='modules') | select('defined') | list }}"
 
 - name: render blackbox exporter configuration
   template: