diff --git a/src/audio_mixer.c b/src/audio_mixer.c
index 8e5126e..ccfba7a 100644
--- a/src/audio_mixer.c
+++ b/src/audio_mixer.c
@@ -242,6 +242,10 @@ static int refill_stream(sts_mixer_sample_t *sample, void *data)
 		}
 	}
 
+	if (r == STS_STREAM_COMPLETE) {
+		ch->voice = -1;
+	}
+
 	return r;
 }
 
diff --git a/subprojects/libsys4 b/subprojects/libsys4
index 5c7da33..529cd10 160000
--- a/subprojects/libsys4
+++ b/subprojects/libsys4
@@ -1 +1 @@
-Subproject commit 5c7da3373389289a363e76a9a862ce8b8d0b9aa2
+Subproject commit 529cd1053ea35a3392f908b03900edacb97ed600