diff --git a/src/sfizz.h b/src/sfizz.h
index 84bb59b1..cb9141fb 100644
--- a/src/sfizz.h
+++ b/src/sfizz.h
@@ -10,6 +10,7 @@
 */
 
 #pragma once
+#include <stddef.h>
 #include <stdbool.h>
 #ifdef __cplusplus
 extern "C" {