diff --git a/api/filtering/db_custom_filters.py b/api/filtering/db_custom_filters.py
index 974f03916..656bfecd0 100644
--- a/api/filtering/db_custom_filters.py
+++ b/api/filtering/db_custom_filters.py
@@ -26,8 +26,10 @@
 # The list of comparators can be seen in POSTGRES_COMPARATOR_LOOKUP
 class OsFilter:
     def __init__(self, name="", comparator="", version=None):
+        os_names = get_valid_os_names()
+
         try:
-            if name and name.lower() not in (os_names := [name.lower() for name in get_valid_os_names()]):
+            if name and name.lower() not in [name.lower() for name in os_names]:
                 raise ValidationException(f"operating_system filter only supports these OS names: {os_names}.")
 
             if version is None: