diff --git a/abilian/services/conversion.py b/abilian/services/conversion.py
index <HASH>..<HASH> 100644
--- a/abilian/services/conversion.py
+++ b/abilian/services/conversion.py
@@ -585,7 +585,7 @@ class CloudoooPdfHandler(Handler):
 
     converted = decodestring(data)
     new_key = hashlib.md5(converted).hexdigest()
-    with open("data/%s.blob" % new_key, "cb") as fd:
+    with open("data/%s.blob" % new_key, "wcb") as fd:
       fd.write(converted)
     return new_key
Bugfix: illegal file open mode.