diff --git a/include/event2/buffer.h b/include/event2/buffer.h
index f6e0e247..2b77b5d1 100644
--- a/include/event2/buffer.h
+++ b/include/event2/buffer.h
@@ -65,6 +65,7 @@ extern "C" {
 #endif
 
 #include <event-config.h>
+#include <stdarg.h>
 
 struct evbuffer;