diff --git a/src/calibre/ebooks/metadata/rar.py b/src/calibre/ebooks/metadata/rar.py
index 28cb092cbc..39f43ca2bd 100644
--- a/src/calibre/ebooks/metadata/rar.py
+++ b/src/calibre/ebooks/metadata/rar.py
@@ -29,7 +29,9 @@ def get_metadata(stream):
                 name, data = extract_member(stream, match=None, name=f)
                 stream = BytesIO(data)
                 stream.name = os.path.basename(name)
-                return get_metadata(stream, stream_type)
+                mi = get_metadata(stream, stream_type)
+                mi.timestamp = None
+                return mi
     raise ValueError('No ebook found in RAR archive')
 
 
diff --git a/src/calibre/ebooks/metadata/zip.py b/src/calibre/ebooks/metadata/zip.py
index 7369d2055c..4a7926339d 100644
--- a/src/calibre/ebooks/metadata/zip.py
+++ b/src/calibre/ebooks/metadata/zip.py
@@ -28,14 +28,16 @@ def get_metadata(stream):
                     with CurrentDir(tdir):
                         path = zf.extract(f)
                         mi = get_metadata(open(path,'rb'), stream_type)
-                        if stream_type == 'opf' and mi.application_id == None:
+                        if stream_type == 'opf' and mi.application_id is None:
                             try:
                                 # zip archive opf files without an application_id were assumed not to have a cover
                                 # reparse the opf and if cover exists read its data from zip archive for the metadata
                                 nmi = zip_opf_metadata(path, zf)
+                                nmi.timestamp = None
                                 return nmi
                             except:
                                 pass
+                        mi.timestamp = None
                         return mi
     raise ValueError('No ebook found in ZIP archive')