diff --git a/osc_out.h b/osc_out.h
index 5c2f3ca..0c29e5e 100644
--- a/osc_out.h
+++ b/osc_out.h
@@ -1,3 +1,4 @@
+#pragma once
 #include "base.h"
 
 typedef struct Oosc_dev Oosc_dev;