diff --git a/src/kyupy/wave_sim.py b/src/kyupy/wave_sim.py
index a5b604c..1549307 100644
--- a/src/kyupy/wave_sim.py
+++ b/src/kyupy/wave_sim.py
@@ -151,7 +151,7 @@ class WaveSim:
                     ops.append((0b0110, o0_idx, i0_idx, i1_idx))
                 elif kind.startswith('xnor'):
                     ops.append((0b1001, o0_idx, i0_idx, i1_idx))
-                elif kind.startswith('not') or kind.startswith('inv'):
+                elif kind.startswith('not') or kind.startswith('inv') or kind.startswith('ibuf'):
                     ops.append((0b0101, o0_idx, i0_idx, i1_idx))
                 elif kind.startswith('buf') or kind.startswith('nbuf'):
                     ops.append((0b1010, o0_idx, i0_idx, i1_idx))