--- a/base/SignalSender.cpp
+++ b/base/SignalSender.cpp
@@ -11,6 +11,7 @@
 #include "SignalSender.h"
 #include "Group.h"
 #include "Behavior.h"
+#include <cstddef>
 
 SignalSender * SignalSender::p_SignalSender = NULL;
 
--- a/base/Behavior.cpp
+++ b/base/Behavior.cpp
@@ -9,6 +9,7 @@
 #include "Private.h"
 #include "Behavior.h"
 #include "Group.h"
+#include <cstddef>
 
 Behavior::Behavior() {
 	//EM_COUT("Behavior::Behavior", 1);
--- a/base/BehaviorVisitor.cpp
+++ b/base/BehaviorVisitor.cpp
@@ -9,6 +9,7 @@
 #include "BehaviorVisitor.h"
 #include "Behavior.h"
 #include "Group.h"
+#include <cstddef>
 
 BehaviorVisitor * BehaviorVisitor::p_BehaviorVisitor = NULL;