diff --git a/anki/media.py b/anki/media.py
index 06fdfadae..11675ba86 100644
--- a/anki/media.py
+++ b/anki/media.py
@@ -259,7 +259,7 @@ If the same name exists, compare checksums."""
     def zipAdded(self):
         "Add files to a zip until over SYNC_ZIP_SIZE. Return zip data."
         f = StringIO()
-        z = zipfile.ZipFile(f, "w")
+        z = zipfile.ZipFile(f, "w", compression=zipfile.ZIP_DEFLATED)
         sz = 0
         cnt = 0
         files = {}
@@ -382,3 +382,8 @@ create table log (fname text primary key, type int);
             if not v[2]:
                 removed.append(k)
         return added, removed
+
+    def sanityCheck(self):
+        assert not self.db.scalar("select count() from log")
+        cnt = self.db.scalar("select count() from media")
+        return cnt
diff --git a/anki/sync.py b/anki/sync.py
index dc71536e4..c1e9a8576 100644
--- a/anki/sync.py
+++ b/anki/sync.py
@@ -577,6 +577,15 @@ class MediaSyncer(object):
             # after server has replied, safe to remove from log
             self.col.media.forgetAdded(fnames)
             self.col.media.setUsn(usn)
+        # step 5: sanity check during beta testing
+        # NOTE: when removing this, need to move server tidyup
+        # back from sanity check to addFiles
+        s = self.server.mediaSanity()
+        c = self.mediaSanity()
+        if c != s:
+            raise Exception("""\
+Sanity check failed. Please copy and paste the text below:\n%s\n%s""" %
+                            (c, s))
         return "success"
 
     def removed(self):
@@ -595,6 +604,9 @@ class MediaSyncer(object):
         "True if zip is the last in set. Server returns new usn instead."
         return self.col.media.syncAdd(zip)
 
+    def mediaSanity(self):
+        return self.col.media.sanityCheck()
+
 # Remote media syncing
 ##########################################################################
 
@@ -615,10 +627,15 @@ class RemoteMediaServer(MediaSyncer, HttpSyncer):
             self.con, "files", StringIO(simplejson.dumps(kw)), self._vars())
 
     def addFiles(self, zip):
+        # no compression, as we compress the zip file instead
         return simplejson.loads(
             self.postData(self.con, "addFiles", StringIO(zip),
                           self._vars(), comp=0))
 
+    def mediaSanity(self):
+        return simplejson.loads(
+            self.postData(self.con, "mediaSanity", None, self._vars()))
+
     # only for unit tests
     def mediatest(self, n):
         return simplejson.loads(