diff --git a/monkey/monkey_island/cc/server_utils/encryptor.py b/monkey/monkey_island/cc/server_utils/encryptor.py
index 4f376532c..83292be8a 100644
--- a/monkey/monkey_island/cc/server_utils/encryptor.py
+++ b/monkey/monkey_island/cc/server_utils/encryptor.py
@@ -27,7 +27,7 @@ class Encryptor:
 
     def _init_key(self, password_file):
         self._cipher_key = Random.new().read(self._BLOCK_SIZE)
-        with open(get_file_descriptor_for_new_secure_file(path=password_file)) as f:
+        with open(get_file_descriptor_for_new_secure_file(path=password_file), "wb") as f:
             f.write(self._cipher_key)
 
     def _load_existing_key(self, password_file):