diff --git a/engine/include/fishbone/client.h b/engine/include/fishbone/client.h
index 891b864..3166f5b 100644
--- a/engine/include/fishbone/client.h
+++ b/engine/include/fishbone/client.h
@@ -5,6 +5,7 @@ namespace fishbone {
 	class Client;
 };
 
+#include <fishbone/machdep.h>
 #include <fishbone/sound.h>
 
 namespace fishbone {
diff --git a/engine/include/fishbone/machdep.h b/engine/include/fishbone/machdep.h
new file mode 100644
index 0000000..20d3c9b
--- /dev/null
+++ b/engine/include/fishbone/machdep.h
@@ -0,0 +1,6 @@
+#ifndef __FISHBONE_MACHDEP_H__
+#define __FISHBONE_MACHDEP_H__
+
+#include <vector>
+
+#endif
diff --git a/engine/include/fishbone/mixer.h b/engine/include/fishbone/mixer.h
index 16fd1fb..edb19b0 100644
--- a/engine/include/fishbone/mixer.h
+++ b/engine/include/fishbone/mixer.h
@@ -5,8 +5,14 @@ namespace fishbone {
 	class Mixer;
 };
 
+#include <fishbone/machdep.h>
+#include <fishbone/sound.h>
+
 namespace fishbone {
 	class Mixer {
+	public:
+		std::vector<fishbone::SoundLoader*> loaders;
+		std::vector<fishbone::Sound*> sounds;
 	};
 }; // namespace fishbone
 
diff --git a/engine/include/fishbone/sound.h b/engine/include/fishbone/sound.h
index 8cb12dc..430415c 100644
--- a/engine/include/fishbone/sound.h
+++ b/engine/include/fishbone/sound.h
@@ -4,8 +4,10 @@
 namespace fishbone {
 	class SoundDriver;
 	class SoundLoader;
+	class Sound;
 }; // namespace fishbone
 
+#include <fishbone/machdep.h>
 #include <fishbone/mixer.h>
 
 namespace fishbone {
@@ -14,6 +16,8 @@ namespace fishbone {
 	};
 	class SoundLoader {
 	};
+	class Sound {
+	};
 }; // namespace fishbone
 
 #endif