diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index d4037b3d5..8bc7b9e6d 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -120,6 +120,22 @@ class AuthError(SynapseError):
         super(AuthError, self).__init__(*args, **kwargs)
 
 
+class GuestAccessError(AuthError):
+    """An error raised when a there is a problem with a guest user accessing
+    a room"""
+
+    def __init__(self, rooms, *args, **kwargs):
+        self.rooms = rooms
+        super(GuestAccessError, self).__init__(*args, **kwargs)
+
+    def error_dict(self):
+        return cs_error(
+            self.msg,
+            self.errcode,
+            rooms=self.rooms,
+        )
+
+
 class EventSizeError(SynapseError):
     """An error raised when an event is too big."""
 
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 38c185cd5..feea407ea 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -16,7 +16,7 @@
 from ._base import BaseHandler
 
 from synapse.api.constants import Membership, EventTypes
-from synapse.api.errors import AuthError
+from synapse.api.errors import GuestAccessError
 from synapse.util import unwrapFirstError
 
 from twisted.internet import defer
@@ -139,10 +139,16 @@ class SyncHandler(BaseHandler):
         """
 
         if sync_config.is_guest:
+            bad_rooms = []
             for room_id in sync_config.filter.list_rooms():
                 world_readable = yield self._is_world_readable(room_id)
                 if not world_readable:
-                    raise AuthError(403, "Guest access not allowed")
+                    bad_rooms.append(room_id)
+
+            if bad_rooms:
+                raise GuestAccessError(
+                    bad_rooms, 403, "Guest access not allowed"
+                )
 
         if timeout == 0 or since_token is None or full_state:
             # we are going to return immediately, so don't bother calling