diff --git a/src/kyupy/circuit.py b/src/kyupy/circuit.py
index d2febf8..8a84e4d 100644
--- a/src/kyupy/circuit.py
+++ b/src/kyupy/circuit.py
@@ -375,7 +375,7 @@ class Circuit:
 
     def io_loc(self, prefix):
         d_top = dict()
-        for i, n in enumerate(self.interface):
+        for i, n in enumerate(list(self.interface) + [n for n in self.nodes if 'ff' in n.kind.lower()]):
             if m := re.match(fr'({prefix}.*?)((?:[_\[\]]\d+)*[_\[\]]*$)', n.name):
                 path = [m[1]] + [int(v) for v in re.split(r'[_\[\]]+', m[2]) if len(v) > 0]
                 d = d_top