diff --git a/src/kyupy/bench.py b/src/kyupy/bench.py
index aeec5a2..a4a514b 100644
--- a/src/kyupy/bench.py
+++ b/src/kyupy/bench.py
@@ -21,7 +21,7 @@ class BenchTransformer(Transformer):
 
     def start(self, _): return self.c
 
-    def parameters(self, args): return [self.c.get_or_add_fork(str(name)) for name in args]
+    def parameters(self, args): return [self.c.get_or_add_fork(str(name)) for name in args if name is not None]
 
     def interface(self, args): self.c.io_nodes.extend(args[0])