diff --git a/lib/libwebsockets.h b/lib/libwebsockets.h
index 9ed8a11f..3c717ff4 100644
--- a/lib/libwebsockets.h
+++ b/lib/libwebsockets.h
@@ -24,6 +24,7 @@
 
 #ifdef __cplusplus
 #include <cstddef>
+#include <cstdarg>
 extern "C" {
 #endif