diff --git a/Framework/Kernel/inc/MantidKernel/Strings.h b/Framework/Kernel/inc/MantidKernel/Strings.h
index 9d2a213e244acc5a6efcaa90bab61615ea9595b3..8420f24f37fee493275ce9aa76c51e99d0382be1 100644
--- a/Framework/Kernel/inc/MantidKernel/Strings.h
+++ b/Framework/Kernel/inc/MantidKernel/Strings.h
@@ -5,6 +5,7 @@
 // Includes
 //----------------------------------------------------------------------
 #include "MantidKernel/DllConfig.h"
+#include "MantidKernel/MultiThreaded.h"
 #include "MantidKernel/StringTokenizer.h"
 #include "MantidKernel/System.h"