diff --git a/doc/arm/_ext/iscconf.py b/doc/arm/_ext/iscconf.py
index b5bd966e2a..1ecd37cb8b 100644
--- a/doc/arm/_ext/iscconf.py
+++ b/doc/arm/_ext/iscconf.py
@@ -47,6 +47,8 @@ def split_csv(argument, required):
             "a non-empty list required; provide at least one value or remove"
             " this option"
         )
+    if not len(outlist) == len(set(outlist)):
+        raise ValueError("duplicate value detected")
     return outlist
 
 
@@ -73,10 +75,8 @@ def domain_factory(domainname, domainlabel, todolist, grammar):
 
         def run(self):
             placeholder = todolist("")
-            placeholder["isc_filter_tags"] = set(self.options.get("filter_tags", []))
-            placeholder["isc_filter_blocks"] = set(
-                self.options.get("filter_blocks", [])
-            )
+            placeholder["isc_filter_tags"] = self.options.get("filter_tags", [])
+            placeholder["isc_filter_blocks"] = self.options.get("filter_blocks", [])
             return [placeholder]
 
     class ISCConfDomain(Domain):
@@ -127,7 +127,7 @@ def domain_factory(domainname, domainlabel, todolist, grammar):
 
             @property
             def isc_tags(self):
-                return set(self.options.get("tags", []))
+                return self.options.get("tags", [])
 
             @property
             def isc_short(self):
@@ -475,11 +475,11 @@ def domain_factory(domainname, domainlabel, todolist, grammar):
                             lambda item: (
                                 (
                                     not acceptable_tags
-                                    or item["tags"].intersection(acceptable_tags)
+                                    or set(item["tags"]).intersection(acceptable_tags)
                                 )
                                 and (
                                     not acceptable_blocks
-                                    or item["block_names"].intersection(
+                                    or set(item["block_names"]).intersection(
                                         acceptable_blocks
                                     )
                                 )