diff --git a/courses/constants.py b/courses/constants.py
index 1f2397c276..76bfbdaebf 100644
--- a/courses/constants.py
+++ b/courses/constants.py
@@ -34,5 +34,5 @@
 
 AVAILABILITY_ANYTIME = "anytime"
 AVAILABILITY_DATED = "dated"
-AVAILABILITY_TYPES = {AVAILABILITY_ANYTIME, AVAILABILITY_DATED}
+AVAILABILITY_TYPES = [AVAILABILITY_ANYTIME, AVAILABILITY_DATED]
 AVAILABILITY_CHOICES = list(zip(AVAILABILITY_TYPES, AVAILABILITY_TYPES))