diff --git a/src/ASM/ElmNorm.h b/src/ASM/ElmNorm.h
index bc0aaca6..5b234a33 100644
--- a/src/ASM/ElmNorm.h
+++ b/src/ASM/ElmNorm.h
@@ -14,6 +14,7 @@
 #ifndef _ELM_NORM_H
 #define _ELM_NORM_H
 
+#include <cstddef>
 #include "LocalIntegral.h"