diff --git a/ov/src/ov_types.h b/ov/src/ov_types.h
index 6d2ad80..11d1589 100644
--- a/ov/src/ov_types.h
+++ b/ov/src/ov_types.h
@@ -19,6 +19,8 @@ extern "C" {
 #include <windows.h>
 #endif
 
+#include <cstddef>
+
   /* automatically detect 64-bit machines */
 
 #ifndef OV_32_BIT