diff --git a/src/calibre/ebooks/metadata/worker.py b/src/calibre/ebooks/metadata/worker.py
index 178174a0d7..909eef05c2 100644
--- a/src/calibre/ebooks/metadata/worker.py
+++ b/src/calibre/ebooks/metadata/worker.py
@@ -35,6 +35,8 @@ def read_metadata_(task, tdir, notification=lambda x,y:x):
             if mi.cover_data:
                 cdata = mi.cover_data[-1]
             mi.cover_data = None
+            if not mi.application_id:
+                mi.application_id = '__calibre_dummy__'
             with open(os.path.join(tdir, '%s.opf'%id), 'wb') as f:
                 f.write(metadata_to_opf(mi))
             if cdata:
diff --git a/src/calibre/gui2/add.py b/src/calibre/gui2/add.py
index becf78e85f..131692a2c2 100644
--- a/src/calibre/gui2/add.py
+++ b/src/calibre/gui2/add.py
@@ -181,6 +181,8 @@ class DBAdder(Thread):
             mi.title = os.path.splitext(name)[0]
         mi.title = mi.title if isinstance(mi.title, unicode) else \
                    mi.title.decode(preferred_encoding, 'replace')
+        if mi.application_id == '__calibre_dummy__':
+            mi.application_id = None
         if self.db is not None:
             if cover:
                 cover = open(cover, 'rb').read()