diff --git a/tasks/main.yml b/tasks/main.yml
index 2c98e0a..65a1b8b 100644
--- a/tasks/main.yml
+++ b/tasks/main.yml
@@ -4,24 +4,40 @@
 - include_tasks: ssh.yml
 - meta: flush_handlers
 
+- fail:
+    msg: 'Invalid `common__iptables__state`: {{ common__iptables__state }}'
+  when: (common__iptables__state != 'purge') and
+        (common__iptables__state != 'install')
 - include_tasks: iptables/purge.yml
   when: common__iptables__state == 'purge'
 - include_tasks: iptables/install.yml
   when: common__iptables__state == 'install'
 - meta: flush_handlers
 
+- fail:
+    msg: 'Invalid `common__certbot__state`: {{ common__certbot__state }}'
+  when: (common__certbot__state != 'purge') and
+        (common__certbot__state != 'install')
 - include_tasks: certbot/purge.yml
   when: common__certbot__state == 'purge'
 - include_tasks: certbot/install.yml
   when: common__certbot__state == 'install'
 - meta: flush_handlers
 
+- fail:
+    msg: 'Invalid `common__apache__state`: {{ common__apache__state }}'
+  when: (common__apache__state != 'purge') and
+        (common__apache__state != 'install')
 - include_tasks: apache/purge.yml
   when: common__apache__state == 'purge'
 - include_tasks: apache/install.yml
   when: common__apache__state == 'install'
 - meta: flush_handlers
 
+- fail:
+    msg: 'Invalid `common__nginx__state`: {{ common__nginx__state }}'
+  when: (common__nginx__state != 'purge') and
+        (common__nginx__state != 'install')
 - include_tasks: nginx/purge.yml
   when: common__nginx__state == 'purge'
 - include_tasks: nginx/install.yml