diff --git a/src/mame/yamaha/ymmu15.cpp b/src/mame/yamaha/ymmu15.cpp
index 8b3deb8389e..89ea335cd72 100644
--- a/src/mame/yamaha/ymmu15.cpp
+++ b/src/mame/yamaha/ymmu15.cpp
@@ -230,4 +230,4 @@ ROM_END
 } // anonymous namespace
 
 
-CONS( 1998, mu15, 0, 0, mu15,  mu15, mu15_state, empty_init, "Yamaha", "MU15", 0 )
+CONS( 1998, mu15, 0, 0, mu15,  mu15, mu15_state, empty_init, "Yamaha", "MU15", MACHINE_NOT_WORKING )