diff --git a/mopidy/backends/local/__init__.py b/mopidy/backends/local/__init__.py
index d42f08ce..0f9b7502 100644
--- a/mopidy/backends/local/__init__.py
+++ b/mopidy/backends/local/__init__.py
@@ -63,6 +63,14 @@ class Library(object):
         """
         return 0
 
+    def tracks(self):
+        """
+        Iterator over all tracks.
+
+        :rtype: :class:`mopidy.models.Track` iterator
+        """
+        raise NotImplementedError
+
     def add(self, track):
         """
         Add the given track to library.
@@ -99,7 +107,7 @@ class Library(object):
 
         :param uri: track URI
         :type uri: string
-        :rtype: list of :class:`mopidy.models.Track`
+        :rtype: :class:`mopidy.models.Track`
         """
         raise NotImplementedError
 
diff --git a/mopidy/backends/local/json.py b/mopidy/backends/local/json.py
index 327f706c..20b922e6 100644
--- a/mopidy/backends/local/json.py
+++ b/mopidy/backends/local/json.py
@@ -56,6 +56,9 @@ class JsonLibrary(local.Library):
         self._tracks = dict((t.uri, t) for t in library.get('tracks', []))
         return len(self._tracks)
 
+    def tracks(self):
+        return self._tracks.itervalues()
+
     def add(self, track):
         self._tracks[track.uri] = track
 
@@ -67,10 +70,9 @@ class JsonLibrary(local.Library):
 
     def lookup(self, uri):
         try:
-            return [self._tracks[uri]]
+            return self._tracks[uri]
         except KeyError:
-            logger.debug('Failed to lookup %r', uri)
-            return []
+            return None
 
     def search(self, query=None, uris=None, exact=False):
         tracks = self._tracks.values()
diff --git a/mopidy/backends/local/library.py b/mopidy/backends/local/library.py
index aeb7736b..eadea027 100644
--- a/mopidy/backends/local/library.py
+++ b/mopidy/backends/local/library.py
@@ -24,7 +24,11 @@ class LocalLibraryProvider(base.BaseLibraryProvider):
     def lookup(self, uri):
         if not self._library:
             return []
-        return self._library.lookup(uri)
+        track = self._library.lookup(uri)
+        if not uri:
+            logger.debug('Failed to lookup %r', uri)
+            return []
+        return [track]
 
     def find_exact(self, query=None, uris=None):
         if not self._library: