diff --git a/frontend/sync-client/src/errors/errors.ts b/frontend/sync-client/src/errors/errors.ts
index 7dc48a3a..6026d692 100644
--- a/frontend/sync-client/src/errors/errors.ts
+++ b/frontend/sync-client/src/errors/errors.ts
@@ -32,3 +32,6 @@ export class FileNotFoundError extends Error {
 export class PermanentSyncError extends Error { }
 
 export class LocalChangesDuringReconciliation extends Error { }
+
+/** The server rejected a checkpoint from a discarded/restored history. */
+export class ServerHistoryChangedError extends Error { }