diff --git a/lib/libwebsockets.h b/lib/libwebsockets.h
index 4a0a7ec2..60e7468c 100644
--- a/lib/libwebsockets.h
+++ b/lib/libwebsockets.h
@@ -24,6 +24,7 @@
 
 #ifdef __cplusplus
 extern "C" {
+#include <cstddef>
 #endif
 
 #ifdef WIN32
@@ -33,6 +34,7 @@ extern "C" {
 #endif
 #include <winsock2.h>
 #include <ws2tcpip.h>
+#include <stddef.h>
 #include "../win32port/win32helpers/websock-w32.h"
 
 #include "../win32port/win32helpers/gettimeofday.h"