diff --git a/README.md b/README.md
index 21e5a39..0196191 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 Code to generate test vectors for various parts of Zcash.
 
-Requires `pyblake2`.
+Requires `pyblake2` and `bitstring`.
 
 `sapling_note_encryption.py` also requires `chacha20poly1305`.