diff --git a/beast/module/core/containers/Array.h b/beast/module/core/containers/Array.h
index 431c457d8c..edcef0320f 100644
--- a/beast/module/core/containers/Array.h
+++ b/beast/module/core/containers/Array.h
@@ -27,6 +27,7 @@
 #include <beast/module/core/containers/ArrayAllocationBase.h>
 #include <beast/module/core/containers/ElementComparator.h>
 #include <beast/module/core/threads/CriticalSection.h>
+#include <beast/Arithmetic.h>
 
 namespace beast {