--- a/src/expr/emptyset.h	2025-04-10 18:42:13.297861573 +0200
+++ b/src/expr/emptyset.h	2025-04-10 18:42:59.042293771 +0200
@@ -20,6 +20,7 @@
 #pragma once
 
 #include <iosfwd>
+#include <cstddef>
 
 namespace CVC4 {
   // messy; Expr needs EmptySet (because it's the payload of a