diff --git a/src/sound.cpp b/src/sound.cpp
--- a/src/sound.cpp
+++ b/src/sound.cpp
@@ -15,11 +15,11 @@
 #include "fileio.h"
 #include "newgrf_sound.h"
 #include "helpers.hpp"
+#include "fios.h"
 
 static uint _file_count;
 static FileEntry *_files;
 
-#define SOUND_SLOT 63
 // Number of levels of panning per side
 #define PANNING_LEVELS 16