diff --git a/libmapper/mapper.h b/libmapper/mapper.h
index 1b37f34..3f86fa6 100644
--- a/libmapper/mapper.h
+++ b/libmapper/mapper.h
@@ -1,3 +1,4 @@
+#pragma once
 #include <systemd/sd-bus.h>
 #include <systemd/sd-event.h>