diff --git a/src/kyupy/logic_sim.py b/src/kyupy/logic_sim.py
index 1c27f42..a74e392 100644
--- a/src/kyupy/logic_sim.py
+++ b/src/kyupy/logic_sim.py
@@ -166,6 +166,8 @@ class LogicSim:
     @staticmethod
     def dff_fct(inputs, outputs):
         logic.bp_buf(outputs[0], inputs[0])
+        if len(outputs) > 1:
+            logic.bp_not(outputs[1], inputs[0])
 
     @staticmethod
     def nand_fct(inputs, outputs):