diff --git a/src/openklant/conf/base.py b/src/openklant/conf/base.py
index a78ad7a..39b7a17 100644
--- a/src/openklant/conf/base.py
+++ b/src/openklant/conf/base.py
@@ -48,7 +48,7 @@
 #
 ADMIN_INDEX_SHOW_REMAINING_APPS_TO_SUPERUSERS = True
 
-CSP_EXCLUDE_URL_PREFIXES += (
+CSP_EXCLUDE_URL_PREFIXES = (
     "/contactgegevens/api/v1/schema/",
     "/klantinteracties/api/v1/schema/",
 )