diff --git a/program/views.py b/program/views.py
index 156553072b39cc5151be7b26a76d98bc09bf71bf..6c19c5327835384b5eb7ef593b42d4e8d368f142 100644
--- a/program/views.py
+++ b/program/views.py
@@ -541,7 +541,7 @@ class APITimeSlotViewSet(viewsets.ModelViewSet):
         # If someone tries to sort by a field that isn't available on the model
         # we silently ignore that and use the default sort order.
         model_fields = [field.name for field in TimeSlot._meta.get_fields()]
-        if order not in model_fields:
+        if order.lstrip('-') not in model_fields:
             order = default_order