diff --git a/runtime/audren.c b/runtime/audren.c
index 407c21f1..f5d9b490 100644
--- a/runtime/audren.c
+++ b/runtime/audren.c
@@ -307,6 +307,8 @@ static void request_update(AudioRenderer *r, const uint8_t *input, uint64_t in_s
             }
         } else
             memcpy(&v, voices + i * voice_stride, sizeof v);
+        // An unused slot can have a zero id. Release its own voice and leave voice zero playing.
+        if (!v.in_use) v.id = (uint32_t)i;
         update_voice(r, &v);
         ServerVoice *server = &r->voices[v.id];
         server->use_float_biquads = (uint8_t)float_voices;
diff --git a/runtime/ipc.c b/runtime/ipc.c
index ba6dd934..1cc4f113 100644
--- a/runtime/ipc.c
+++ b/runtime/ipc.c
@@ -695,7 +695,7 @@ static void update_build(Update *u, int first) {
     memcpy(w, &h, sizeof h);
     w += sizeof h + h.behavior + h.memory_pools + h.voice_resources;
     for (int i = 0; i < p->voice_count; i++) {
-        AudrenVoiceIn v = {.id = (uint32_t)i};
+        AudrenVoiceIn v = {0};   // the client leaves the id of an unused slot zero
         if (i == 0) {   // one PCM16 voice with a 100 ms buffer: consumed after 20 frames
             v = (AudrenVoiceIn){.id = 0, .is_new = (uint8_t)first, .in_use = 1, .play_state = PLAY_STARTED,
                                 .sample_format = FMT_PCM16, .sample_rate = 48000, .channel_count = 1, .pitch = 1,