diff --git a/indexlib/memvector.h b/indexlib/memvector.h
index 680d2874..d4cc446e 100644
--- a/indexlib/memvector.h
+++ b/indexlib/memvector.h
@@ -43,6 +43,7 @@
 #include <iostream>
 #include <iterator>
 #include <string>
+#include <cstddef>
 #include <cstring>
 #include <assert.h>