diff --git a/MantidPlot/src/Process.cpp b/MantidPlot/src/Process.cpp
index b9dc2d4aec4a298a9c6da4f8b3951ba1745de8b7..7488afe00e9ac9ac826fdc6fae0fdb691b15640b 100644
--- a/MantidPlot/src/Process.cpp
+++ b/MantidPlot/src/Process.cpp
@@ -11,6 +11,7 @@
 #include <Psapi.h>
 #include "MantidQtWidgets/Common/QStringUtils.h"
 #elif defined(Q_OS_MAC)
+#include <cstdlib>
 #include <libproc.h>
 #include <sys/sysctl.h>
 #endif