diff --git a/src/modulator.h b/src/modulator.h
index f091753..8b2884e 100644
--- a/src/modulator.h
+++ b/src/modulator.h
@@ -1,3 +1,4 @@
+#pragma once
 #include "common.h"
 #include "rds.h"
 #include "waveforms.h"