diff --git a/docker/frontend/src/engine/library.ts b/docker/frontend/src/engine/library.ts
index 79f3ef1..128b74f 100644
--- a/docker/frontend/src/engine/library.ts
+++ b/docker/frontend/src/engine/library.ts
@@ -1017,7 +1017,10 @@ async function clearWalk(folder: string): Promise<void> {
 async function framesAt(root: FileSystemDirectoryHandle, rels: string[]): Promise<WalkFile[]> {
   const dirs = new Map<string, FileSystemDirectoryHandle>();
   const out: WalkFile[] = [];
-  for (const rel of rels) {
+  for (const raw of rels) {
+    // A walk file written on Windows spells its frame `2017\2017-02-PHUNINH\_DSF1.RAF`;
+    // normalising once here means everything below sees the same `/` as the rest of the catalogue.
+    const rel = normPath(raw);
     const cut = rel.lastIndexOf('/');
     const at = cut < 0 ? '' : rel.slice(0, cut);
     let dir = dirs.get(at);
diff --git a/docker/frontend/src/engine/libraryBackup.ts b/docker/frontend/src/engine/libraryBackup.ts
index 1ba0d78..1941fca 100644
--- a/docker/frontend/src/engine/libraryBackup.ts
+++ b/docker/frontend/src/engine/libraryBackup.ts
@@ -28,6 +28,7 @@ import {
   listEdits,
   listFolders,
   listPhotos,
+  normPath,
   renameFolder,
   restoreCatalogue,
   setBackupTileFetcher,
@@ -53,7 +54,9 @@ export async function readBackupTile(id: string): Promise<Blob | null> {
   try {
     const root = await folderHandle();
     if (!root) return null;
-    const parts = id.split('/');
+    // A frame id is `folder/dir/name`; a Windows-written one can say `\`, so it is
+    // spelled the same way here as everywhere else before it is cut.
+    const parts = normPath(id).split('/');
     const name = parts.pop() as string;
     const dir = await at(root, [THUMBS, ...parts].join('/'));
     const file = await dir.getFileHandle(spell(name));
@@ -274,7 +277,8 @@ async function at(root: FileSystemDirectoryHandle, rel: string, create = false):
   if (!cache) opened.set(root, (cache = new Map()));
   let node = root;
   let path = '';
-  for (const part of rel.split('/')) {
+  // Both separators: a path handed in from a Windows-written id may say `\`.
+  for (const part of rel.split(/[\\/]/)) {
     if (!part) continue;
     const name = spell(part);
     path = path ? `${path}/${name}` : name;
@@ -345,7 +349,7 @@ export async function backupNow(onProgress?: (p: BackupProgress) => void): Promi
     const blob = photo.thumb ?? (await getPhotoThumb(photo.id));
     if (!blob) continue;
     if (had.get(photo.id) === blob.size) continue;
-    const parts = photo.id.split('/');
+    const parts = normPath(photo.id).split('/');
     parts.pop();
     const rel = [THUMBS, ...parts, photo.name].join('/');
     try {
diff --git a/docker/frontend/src/engine/rollWalk.ts b/docker/frontend/src/engine/rollWalk.ts
index 4da1055..0ebbaac 100644
--- a/docker/frontend/src/engine/rollWalk.ts
+++ b/docker/frontend/src/engine/rollWalk.ts
@@ -52,7 +52,9 @@ export const SYSTEM_DIR = /^[.@]|^\$RECYCLE\.BIN$|^RECYCLER$|^System Volume Info
 export async function openAt(root: FileSystemDirectoryHandle, rel: string): Promise<FileSystemDirectoryHandle | null> {
   let dir = root;
   try {
-    for (const part of rel.split('/').filter(Boolean)) dir = await dir.getDirectoryHandle(part);
+    // ponytail: a path written on Windows can arrive with `\`, so both separators
+    // split it; a POSIX name holding a literal `\` is the price (normPath pays it already).
+    for (const part of rel.split(/[\\/]/).filter(Boolean)) dir = await dir.getDirectoryHandle(part);
   } catch {
     return null;
   }