diff --git a/jupyter_collaboration/handlers.py b/jupyter_collaboration/handlers.py
index acbe9043..438a4ee7 100644
--- a/jupyter_collaboration/handlers.py
+++ b/jupyter_collaboration/handlers.py
@@ -134,10 +134,10 @@ async def open(self, room_id):
             # Close websocket and propagate error.
             if isinstance(e, web.HTTPError):
                 self.log.error(f"File {path} not found.\n{e!r}", exc_info=e)
-                self.close(1004, f"File {path} not found.")
+                self.close(4000, f"File {path} not found.")
             else:
                 self.log.error(f"Error initializing: {path}\n{e!r}", exc_info=e)
-                self.close(1005, f"Error initializing: {path}. You need to close the document.")
+                self.close(4001, f"Error initializing: {path}. You need to close the document.")
 
             # Clean up the room and delete the file loader
             if self.room is not None and len(self.room.clients) == 0 or self.room.clients == [self]:
@@ -155,7 +155,7 @@ async def open(self, room_id):
                 f"Client tried to connect to {self._room_id} with an expired session ID {session_id}."
             )
             self.close(
-                1003,
+                4002,
                 f"Document session {session_id} expired. You need to reload this browser tab.",
             )
 
diff --git a/packages/docprovider/src/yprovider.ts b/packages/docprovider/src/yprovider.ts
index 0f6887f2..c87e4484 100644
--- a/packages/docprovider/src/yprovider.ts
+++ b/packages/docprovider/src/yprovider.ts
@@ -136,7 +136,7 @@ export class WebSocketProvider implements IDocumentProvider {
   }
 
   private _onConnectionClosed = (event: any): void => {
-    if (event.code >= 1003 && event.code < 1006) {
+    if (event.code >= 4000 && event.code < 4005) {
       console.error('Document provider closed:', event.code, event.reason);
 
       showErrorMessage(this._trans.__('Document error'), event.reason, [