diff --git a/src/libCom/cxxTemplates/epicsSingleton.h b/src/libCom/cxxTemplates/epicsSingleton.h
index b97c82b8c..cece8007c 100644
--- a/src/libCom/cxxTemplates/epicsSingleton.h
+++ b/src/libCom/cxxTemplates/epicsSingleton.h
@@ -19,6 +19,7 @@
 #define epicsSingleton_h
 
 #include <new>
+#include <cstddef>
 
 #include "shareLib.h"
 #include "epicsAssert.h"