diff --git a/src/RTCSession/ReferSubscriber.js b/src/RTCSession/ReferSubscriber.js
index 91d4065c..54a2e681 100644
--- a/src/RTCSession/ReferSubscriber.js
+++ b/src/RTCSession/ReferSubscriber.js
@@ -35,9 +35,19 @@ module.exports = class ReferSubscriber extends EventEmitter {
 		let replaces = null;
 
 		if (options.replaces) {
-			replaces = options.replaces._request.call_id;
-			replaces += `;to-tag=${options.replaces._to_tag}`;
-			replaces += `;from-tag=${options.replaces._from_tag}`;
+			const dialog = options.replaces._dialog;
+
+			// RFC 3891 section 3: to-tag is the remote tag and from-tag the local
+			// tag of the dialog to replace, whoever sent the initial INVITE.
+			if (dialog) {
+				replaces = dialog.id.call_id;
+				replaces += `;to-tag=${dialog.id.remote_tag}`;
+				replaces += `;from-tag=${dialog.id.local_tag}`;
+			} else {
+				replaces = options.replaces._request.call_id;
+				replaces += `;to-tag=${options.replaces._to_tag}`;
+				replaces += `;from-tag=${options.replaces._from_tag}`;
+			}
 
 			replaces = encodeURIComponent(replaces);
 		}
diff --git a/src/test/test-ReferSubscriber.ts b/src/test/test-ReferSubscriber.ts
new file mode 100644
index 00000000..451e8deb
--- /dev/null
+++ b/src/test/test-ReferSubscriber.ts
@@ -0,0 +1,71 @@
+import './include/common';
+
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+const ReferSubscriber = require('../RTCSession/ReferSubscriber.js');
+
+const TARGET = 'sip:bob@example.com';
+const CALL_ID = 'a84b4c76e66710';
+const LOCAL_TAG = 'localtag';
+const REMOTE_TAG = 'remotetag';
+
+// Session to replace, with the fields set by RTCSession once its dialog is
+// confirmed.
+function createReplacedSession(direction: 'outgoing' | 'incoming'): object {
+	const outgoing = direction === 'outgoing';
+
+	return {
+		_request: { call_id: CALL_ID },
+		// Tags of the From and To header fields of the initial INVITE.
+		_from_tag: outgoing ? LOCAL_TAG : REMOTE_TAG,
+		_to_tag: outgoing ? REMOTE_TAG : LOCAL_TAG,
+		_dialog: {
+			id: { call_id: CALL_ID, local_tag: LOCAL_TAG, remote_tag: REMOTE_TAG },
+		},
+	};
+}
+
+// Sends a REFER that replaces the given session and returns its Refer-To
+// header field.
+function sendRefer(replaces: object): string | undefined {
+	let extraHeaders: string[] = [];
+
+	const session = {
+		contact: '<sip:alice@example.com;transport=ws>',
+		_ua: {
+			_configuration: {
+				uri: { scheme: 'sip', user: 'alice', host: 'example.com' },
+			},
+		},
+		sendRequest(_method: string, options: { extraHeaders: string[] }) {
+			extraHeaders = options.extraHeaders;
+
+			return { cseq: 1 };
+		},
+	};
+
+	new ReferSubscriber(session).sendRefer(TARGET, { replaces });
+
+	return extraHeaders.find(header => header.startsWith('Refer-To:'));
+}
+
+describe('ReferSubscriber', () => {
+	test('Replaces of an outgoing session', () => {
+		expect(sendRefer(createReplacedSession('outgoing'))).toBe(
+			'Refer-To: <sip:bob@example.com?Replaces=a84b4c76e66710%3Bto-tag%3Dremotetag%3Bfrom-tag%3Dlocaltag>'
+		);
+	});
+
+	test('Replaces of an incoming session', () => {
+		expect(sendRefer(createReplacedSession('incoming'))).toBe(
+			'Refer-To: <sip:bob@example.com?Replaces=a84b4c76e66710%3Bto-tag%3Dremotetag%3Bfrom-tag%3Dlocaltag>'
+		);
+	});
+
+	test('Replaces of a session without dialog', () => {
+		const replaces = { ...createReplacedSession('outgoing'), _dialog: null };
+
+		expect(sendRefer(replaces)).toBe(
+			'Refer-To: <sip:bob@example.com?Replaces=a84b4c76e66710%3Bto-tag%3Dremotetag%3Bfrom-tag%3Dlocaltag>'
+		);
+	});
+});