diff --git a/netdev/tree_match.py b/netdev/tree_match.py
index 4c383dc..76dc403 100644
--- a/netdev/tree_match.py
+++ b/netdev/tree_match.py
@@ -11,8 +11,8 @@
 
 def series_tree_name_direct(conf_trees, series):
     for t in conf_trees:
-        if re.match(r'\[.*{pfx}.*\]'.format(pfx=t), series.subject):
-            return t
+        if re.match(rf'\[.*{t.pfx}.*\]', series.subject):
+            return t.name
 
 
 def _file_name_match_start(pfx, fn):
diff --git a/pw_poller.py b/pw_poller.py
index f964f9c..9be6acc 100755
--- a/pw_poller.py
+++ b/pw_poller.py
@@ -96,7 +96,7 @@ def init_state_from_disk(self) -> None:
             pass
 
     def _series_determine_tree(self, s: PwSeries) -> str:
-        s.tree_name = self.list_module.series_tree_name_direct(self._trees.keys(), s)
+        s.tree_name = self.list_module.series_tree_name_direct(self._trees.values(), s)
         s.tree_mark_expected = True
         s.tree_marked = bool(s.tree_name)