diff --git a/src/kyupy/techlib.py b/src/kyupy/techlib.py
index 21c82a6..0ceb8cc 100644
--- a/src/kyupy/techlib.py
+++ b/src/kyupy/techlib.py
@@ -31,7 +31,8 @@ class TechLib:
         """Returns a pin list position for a given node kind and pin name."""
         if kind[:3] in ('OAI', 'AOI'):
             if pin[0] == 'A': return int(pin[1]) - 1
-            if pin[0] == 'B': return int(pin[1]) + int(kind[4]) - 1
+            if pin == 'B': return int(kind[3])
+            if pin[0] == 'B': return int(pin[1]) - 1 + int(kind[3])
         for prefix, pins, index in [('HADD', ('B0', 'SO'), 1),
                                     ('MUX21', ('S', 'S0'), 2),
                                     ('MX2', ('S0',), 2),