diff --git a/adb/sign_cryptography.py b/adb/sign_cryptography.py
index 31a9ef7..0f75514 100644
--- a/adb/sign_cryptography.py
+++ b/adb/sign_cryptography.py
@@ -30,7 +30,7 @@ def __init__(self, rsa_key_path):
 
         with open(rsa_key_path) as rsa_prv_file:
             self.rsa_key = serialization.load_pem_private_key(
-                    rsa_prv_file.read(), None, default_backend())
+                    rsa_prv_file.read().encode(), None, default_backend())
 
     def Sign(self, data):
         return self.rsa_key.sign(