diff --git a/bin/readSyncMessageFork.js b/bin/readSyncMessageFork.js
new file mode 100644
index 0000000..9bb09ab
--- /dev/null
+++ b/bin/readSyncMessageFork.js
@@ -0,0 +1,31 @@
+// @ts-nocheck
+const syncProtocol = require('y-protocols/dist/sync.cjs')
+
+const decoding = require('lib0/dist/decoding.cjs')
+
+/**
+ * @param {decoding.Decoder} decoder A message received from another client
+ * @param {encoding.Encoder} encoder The reply message. Will not be sent if empty.
+ * @param {Y.Doc} doc
+ * @param {boolean} readOnly If true, updates will be silently ignored instead of applied.
+ * @param {any} transactionOrigin
+ */
+const readSyncMessage = (decoder, encoder, doc, readOnly = false, transactionOrigin) => {
+  const messageType = decoding.readVarUint(decoder)
+  switch (messageType) {
+    case syncProtocol.messageYjsSyncStep1:
+      syncProtocol.readSyncStep1(decoder, encoder, doc)
+      break
+    case syncProtocol.messageYjsSyncStep2:
+      if (!readOnly) syncProtocol.readSyncStep2(decoder, doc, transactionOrigin)
+      break
+    case syncProtocol.messageYjsUpdate:
+      if (!readOnly) syncProtocol.readUpdate(decoder, doc, transactionOrigin)
+      break
+    default:
+      throw new Error('Unknown message type')
+  }
+  return messageType
+}
+
+module.exports = { readSyncMessage }
diff --git a/bin/utils.js b/bin/utils.js
index d9c1543..d79acab 100644
--- a/bin/utils.js
+++ b/bin/utils.js
@@ -12,6 +12,7 @@ const debounce = require('lodash.debounce')
 
 const callbackHandler = require('./callback.js').callbackHandler
 const isCallbackSet = require('./callback.js').isCallbackSet
+const readSyncMessage = require('./readSyncMessageFork.js').readSyncMessage
 
 const CALLBACK_DEBOUNCE_WAIT = parseInt(process.env.CALLBACK_DEBOUNCE_WAIT) || 2000
 const CALLBACK_DEBOUNCE_MAXWAIT = parseInt(process.env.CALLBACK_DEBOUNCE_MAXWAIT) || 10000
@@ -181,7 +182,7 @@ const messageListener = async (conn, doc, message) => {
         await doc.whenSynced
       }
       encoding.writeVarUint(encoder, messageSync)
-      syncProtocol.readSyncMessage(decoder, encoder, doc, null)
+      readSyncMessage(decoder, encoder, doc, conn.readOnly, null)
       if (encoding.length(encoder) > 1) {
         send(doc, conn, encoding.toUint8Array(encoder))
       }