diff --git a/setup.py b/setup.py
index 4f8818f5..80b57ea3 100755
--- a/setup.py
+++ b/setup.py
@@ -58,6 +58,7 @@ setup(
 
         # numerics
         'arrow',  # better datetimes
+        'bidict',  # 2 way map
         'cython',
         'numpy',
         'numba',