diff --git a/eismultiplexer.h b/eismultiplexer.h
index e5cb1ef..7fa36d6 100644
--- a/eismultiplexer.h
+++ b/eismultiplexer.h
@@ -28,7 +28,7 @@
 #pragma once
 
 #include <stdint.h>
-#include <semaphore.h>
+#include <stddef.h>
 #include <stdbool.h>
 
 /**