diff --git a/src/beast/beast/module/core/containers/Array.h b/src/beast/beast/module/core/containers/Array.h
index 431c457d8..edcef0320 100644
--- a/src/beast/beast/module/core/containers/Array.h
+++ b/src/beast/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 {