diff --git a/src/libserver/css/css_selector.hxx b/src/libserver/css/css_selector.hxx
index 1e5f5bb13..59f7bbbe7 100644
--- a/src/libserver/css/css_selector.hxx
+++ b/src/libserver/css/css_selector.hxx
@@ -24,6 +24,7 @@
 #include <optional>
 #include <vector>
 #include <functional>
+#include <memory>
 #include "parse_error.hxx"
 #include "css_tokeniser.hxx"
 #include "html_tags.h"