diff --git a/include/dolphin/os.h b/include/dolphin/os.h
index e9525f63..5b581565 100644
--- a/include/dolphin/os.h
+++ b/include/dolphin/os.h
@@ -150,6 +150,7 @@ void OSFatal(GXColor fg, GXColor bg, const char* msg);
 #endif
 
 #include <dolphin/os/OSAlarm.h>
+#include <dolphin/os/OSArena.h>
 #include <dolphin/os/OSCache.h>
 #include <dolphin/os/OSContext.h>
 #include <dolphin/os/OSError.h>