diff --git a/pkg/sip/media_port.go b/pkg/sip/media_port.go
index 10875886..b2d2767e 100644
--- a/pkg/sip/media_port.go
+++ b/pkg/sip/media_port.go
@@ -405,8 +405,14 @@ type MediaPort interface {
 	GetOutboundDTMFWriter() msdk.WriteCloser[*livekit.SipDTMF]
 
 	// WriteInboundAudioTo tells port where to write inbound SIP audio.
+	//
+	// MediaPort.Close() will propagate to the argument writer. The caller is
+	// responsible for closing the returned media writer.
 	WriteInboundAudioTo(w msdk.PCM16Writer) msdk.PCM16Writer
+
 	// WriteInboundDTMFTo tells port where to write inbound SIP DTMF.
+	//
+	// Has similar close semantics to WriteInboundAudioTo (see comment above).
 	WriteInboundDTMFTo(w msdk.WriteCloser[*livekit.SipDTMF]) msdk.WriteCloser[*livekit.SipDTMF]
 
 	// If there is no offer, this generates an offer.
@@ -735,7 +741,6 @@ func (p *mediaPort) GetOutboundAudioWriter() msdk.PCM16Writer {
 	return p.audioOut
 }
 
-// WriteInboundAudioTo sets audio writer that will receive decoded PCM from incoming RTP packets.
 func (p *mediaPort) WriteInboundAudioTo(w msdk.PCM16Writer) msdk.PCM16Writer {
 	return p.audioIn.Swap(w)
 }
diff --git a/pkg/sip/outbound.go b/pkg/sip/outbound.go
index 2cf4f36a..1ced80fc 100644
--- a/pkg/sip/outbound.go
+++ b/pkg/sip/outbound.go
@@ -560,6 +560,9 @@ func (c *outboundCall) connectMedia() {
 		old.Close()
 		c.log.Warnw("media port has unexpected inbound audio writer", nil)
 	}
+	// WriteInboundAudioTo takes ownership of c.lkRoomIn, so nil it out to avoid
+	// double-closing later.
+	c.lkRoomIn = nil
 
 	if old := c.media.WriteInboundDTMFTo(c.lkRoom.GetInboundDTMFWriter()); old != nil {
 		old.Close()