diff --git a/src/spectrum/model/spectrum-model.h b/src/spectrum/model/spectrum-model.h
index b56a85340..add359f28 100644
--- a/src/spectrum/model/spectrum-model.h
+++ b/src/spectrum/model/spectrum-model.h
@@ -22,6 +22,7 @@
 
 #include <ns3/simple-ref-count.h>
 
+#include <cstddef>
 #include <vector>
 
 namespace ns3