diff --git a/cps/tasks/thumbnail.py b/cps/tasks/thumbnail.py
index cc847274..884ae0c3 100644
--- a/cps/tasks/thumbnail.py
+++ b/cps/tasks/thumbnail.py
@@ -197,7 +197,8 @@ class TaskGenerateCoverThumbnails(CalibreTask):
                             img.format = thumbnail.format
                             img.save(filename=filename)
                         else:
-                            with open(filename, 'rb') as fd:
+                            stream.seek(0)
+                            with open(filename, 'wb') as fd:
                                 copyfileobj(stream, fd)
 
                 except Exception as ex: