diff --git a/src/mame/includes/metro.h b/src/mame/includes/metro.h
index fbea40970ff..eee69a17f72 100644
--- a/src/mame/includes/metro.h
+++ b/src/mame/includes/metro.h
@@ -81,9 +81,9 @@ public:
 
 	/* devices */
 	required_device<cpu_device> maincpu;
-	required_device<cpu_device> audiocpu;
+	optional_device<cpu_device> audiocpu;
 	optional_device<okim6295_device> oki;
-	required_device<device_t> ymsnd;
+	optional_device<device_t> ymsnd;
 	optional_device<k053936_device> k053936;
 };
 
diff --git a/src/mame/includes/mitchell.h b/src/mame/includes/mitchell.h
index b77efcc8931..3edda2e41d3 100644
--- a/src/mame/includes/mitchell.h
+++ b/src/mame/includes/mitchell.h
@@ -38,7 +38,7 @@ public:
 
 	/* devices */
 	optional_device<cpu_device> audiocpu;
-	required_device<okim6295_device> oki;
+	optional_device<okim6295_device> oki;
 };