diff --git a/lib/mnemonic.py b/lib/mnemonic.py
index 43ccf0c0f..0f8e853f7 100644
--- a/lib/mnemonic.py
+++ b/lib/mnemonic.py
@@ -62,6 +62,7 @@ class Mnemonic(object):
     @classmethod
     def mnemonic_to_seed(self, mnemonic, passphrase):
         PBKDF2_ROUNDS = 2048
+        mnemonic = self.prepare_seed(mnemonic)
         return pbkdf2.PBKDF2(mnemonic, 'mnemonic' + passphrase, iterations = PBKDF2_ROUNDS, macmodule = hmac, digestmodule = hashlib.sha512).read(64)
 
     @classmethod