diff --git a/quiche/common/platform/default/quiche_platform_impl/quiche_iovec_impl.h b/quiche/common/platform/default/quiche_platform_impl/quiche_iovec_impl.h
index b4ac17f..ce32ada 100644
--- a/quiche/common/platform/default/quiche_platform_impl/quiche_iovec_impl.h
+++ b/quiche/common/platform/default/quiche_platform_impl/quiche_iovec_impl.h
@@ -10,10 +10,14 @@
 #if defined(_WIN32)
 
 // See <https://pubs.opengroup.org/onlinepubs/009604599/basedefs/sys/uio.h.html>
+#ifndef _IOVEC_DEFINED_
+#define _IOVEC_DEFINED_
+#define _STRUCT_IOVEC
 struct QUICHE_EXPORT iovec {
   void* iov_base;
   size_t iov_len;
 };
+#endif
 
 #else