diff --git a/src/kyupy/circuit.py b/src/kyupy/circuit.py
index aee1191..11ef657 100644
--- a/src/kyupy/circuit.py
+++ b/src/kyupy/circuit.py
@@ -631,8 +631,8 @@ class Circuit:
                     queue.append(succ)
             yield n
 
-    def fanout_free_regions(self):
-        for stem in self.reversed_topological_order():
+    def fanout_free_regions(self, tlib: 'TechLib'): # type: ignore
+        for stem in self.reversed_topological_order(tlib):
             if len(stem.outs) == 1 and 'dff' not in stem.kind.lower(): continue
             region = []
             if 'dff' in stem.kind.lower():