diff --git a/src/tools/qvaluevector.h b/src/tools/qvaluevector.h
index 7fe13a4..56fa53f 100644
--- a/src/tools/qvaluevector.h
+++ b/src/tools/qvaluevector.h
@@ -39,6 +39,8 @@
 #ifndef QVALUEVECTOR_H
 #define QVALUEVECTOR_H
 
+#include <cstddef>
+
 #ifndef QT_H
 #include "qtl.h"
 #include "qshared.h"