diff --git a/src/serialize.h b/src/serialize.h
index cb3a3ea0..c2bfa278 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -34,6 +34,7 @@ typedef unsigned long long  uint64;
 // Note that VirtualLock does not provide this as a guarantee on Windows,
 // but, in practice, memory that has been VirtualLock'd almost never gets written to
 // the pagefile except in rare circumstances where memory is extremely low.
+#include <windows.h>
 #define mlock(p, n) VirtualLock((p), (n));
 #define munlock(p, n) VirtualUnlock((p), (n));
 #else