diff --git a/core/utils.c b/core/utils.c
index 69b68b14..070f49c4 100644
--- a/core/utils.c
+++ b/core/utils.c
@@ -2225,6 +2225,7 @@ struct uwsgi_string_list *uwsgi_string_new_list(struct uwsgi_string_list **list,
 	uwsgi_string->next = NULL;
 	uwsgi_string->custom = 0;
 	uwsgi_string->custom2 = 0;
+	uwsgi_string->custom_ptr = NULL;
 
 	return uwsgi_string;
 }