diff --git a/src/mongocxx/lib/mongocxx/private/mock.hh b/src/mongocxx/lib/mongocxx/private/mock.hh
index 1726280d34..c5dcfe5ddf 100644
--- a/src/mongocxx/lib/mongocxx/private/mock.hh
+++ b/src/mongocxx/lib/mongocxx/private/mock.hh
@@ -16,8 +16,11 @@
 
 #include <bsoncxx/v1/detail/macros.hpp>
 
+#include <mongocxx/v1/config/export.hpp>
+
 #include <array>
 #include <cassert>
+#include <cstddef>
 #include <functional>
 #include <iostream>
 #include <memory>