diff --git a/NPLib/Core/NPDetectorFactory.cxx b/NPLib/Core/NPDetectorFactory.cxx
index 1fe9e31ae56fdb33d8ca126029abfa07d9e27de8..961f9bc645e7baa5606289e165fdfb206d546f97 100644
--- a/NPLib/Core/NPDetectorFactory.cxx
+++ b/NPLib/Core/NPDetectorFactory.cxx
@@ -3,6 +3,8 @@ using namespace NPA;
 #include<dlfcn.h>
 #include<fstream>
 #include<iostream>
+#include<stdlib.h>
+
 DetectorFactory* DetectorFactory::m_Instance = 0;
 #ifdef __linux__
 std::string SHARED_LIB_EXTENSION = ".so";