diff --git a/spotipy/oauth2.py b/spotipy/oauth2.py
index 3e79e5a..b339918 100644
--- a/spotipy/oauth2.py
+++ b/spotipy/oauth2.py
@@ -153,8 +153,10 @@ class SpotifyOAuth(object):
                 pass
 
     def _is_scope_subset(self, needle_scope, haystack_scope):
-        needle_scope = set(needle_scope.split())
-        haystack_scope = set(haystack_scope.split())
+        if needle_scope:
+            needle_scope = set(needle_scope.split())
+        if haystack_scope:
+            haystack_scope = set(haystack_scope.split())
 
         return needle_scope <= haystack_scope