diff --git a/src/direwolf.h b/src/direwolf.h
index efc329b..dff9dea 100644
--- a/src/direwolf.h
+++ b/src/direwolf.h
@@ -37,6 +37,7 @@
 
 #endif
 
+#include <stddef.h>
 
 /*
  * Previously, we could handle only a single audio device.