diff --git a/pyppd/archiver.py b/pyppd/archiver.py
index 1de90c0..a5e44c1 100644
--- a/pyppd/archiver.py
+++ b/pyppd/archiver.py
@@ -44,7 +44,7 @@ def compress(directory):
     returns a compressed pickle dump of it.
 
     """
-    ppds = b""
+    ppds = bytearray()
     ppds_index = {}
     abs_directory = os.path.abspath(directory)