diff --git a/src/CommonItemSet.hh b/src/CommonItemSet.hh
index adf3c9a0..667e1aa6 100644
--- a/src/CommonItemSet.hh
+++ b/src/CommonItemSet.hh
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <array>
 #include <phosg/Encoding.hh>
 
 #include "GSLArchive.hh"