diff --git a/util/arena.h b/util/arena.h
index fa01a49443b8be8098dcba27cd5d50ece1b50548..9149498c877865aaf6fbaf42e65ea965caa1f2a0 100644
--- a/util/arena.h
+++ b/util/arena.h
@@ -12,6 +12,9 @@
 // size, it uses malloc to directly get the requested size.
 
 #pragma once
+#ifndef OS_WIN
+#include <sys/mman.h>
+#endif
 #include <cstddef>
 #include <cerrno>
 #include <vector>