diff --git a/src/handlers/ciphers.ts b/src/handlers/ciphers.ts
index 8a4bc27..73a8653 100644
--- a/src/handlers/ciphers.ts
+++ b/src/handlers/ciphers.ts
@@ -32,6 +32,7 @@ import { auditRequestMetadata, writeAuditEvent } from '../services/audit-events'
 // attachments, import/export, and current official clients.
 export interface CipherResponseOptions {
   preserveRepairableUris?: boolean;
+  validFolderIds?: ReadonlySet<string>;
 }
 
 export function shouldPreserveRepairableCipherUris(request: Request): boolean {
@@ -48,6 +49,12 @@ function normalizeOptionalId(value: unknown): string | null {
   return normalized ? normalized : null;
 }
 
+function normalizeResponseFolderId(folderId: unknown, validFolderIds?: ReadonlySet<string>): string | null {
+  const normalized = normalizeOptionalId(folderId);
+  if (!normalized) return null;
+  return validFolderIds && !validFolderIds.has(normalized) ? null : normalized;
+}
+
 function readBooleanOrFallback(value: unknown, fallback: boolean): boolean {
   return typeof value === 'boolean' ? value : fallback;
 }
@@ -727,7 +734,7 @@ export function cipherToResponse(
     // Pass through ALL stored cipher fields (known + unknown)
     ...passthrough,
     // Server-computed / enforced fields (always override)
-    folderId: normalizeOptionalId(cipher.folderId),
+    folderId: normalizeResponseFolderId(cipher.folderId, options.validFolderIds),
     type: Number(cipher.type) || 1,
     organizationId: normalizeOptionalId((passthrough as any).organizationId ?? null),
     organizationUseTotp: !!((passthrough as any).organizationUseTotp ?? false),
@@ -785,9 +792,10 @@ export async function handleGetCiphers(request: Request, env: Env, userId: strin
   const attachmentsByCipher = await storage.getAttachmentsByCipherIds(
     filteredCiphers.map((cipher) => cipher.id)
   );
+  const validFolderIds = new Set((await storage.getAllFolders(userId)).map((folder) => folder.id));
 
   // Build responses only for the current page to keep pagination cheap.
-  const responseOptions = cipherResponseOptionsForRequest(request);
+  const responseOptions = { ...cipherResponseOptionsForRequest(request), validFolderIds };
   const cipherResponses: CipherResponse[] = [];
   for (const cipher of filteredCiphers) {
     const attachments = attachmentsByCipher.get(cipher.id) || [];
diff --git a/src/handlers/sync.ts b/src/handlers/sync.ts
index 1ea0125..dbbca5b 100644
--- a/src/handlers/sync.ts
+++ b/src/handlers/sync.ts
@@ -88,12 +88,13 @@ export async function handleSync(request: Request, env: Env, userId: string): Pr
     .map(buildWebAuthnPrfOption)
     .filter((option): option is NonNullable<typeof option> => !!option);
   const userDecryptionOptions = buildUserDecryptionOptions(user, webAuthnPrfOptions[0] || null);
+  const validFolderIds = new Set(folders.map((folder) => folder.id));
 
   const profile: ProfileResponse = buildProfileResponse(user, env);
 
   const cipherResponses: CipherResponse[] = [];
   for (const cipher of ciphers) {
-    const response = cipherToResponse(cipher, attachmentsByCipher.get(cipher.id) || [], { preserveRepairableUris });
+    const response = cipherToResponse(cipher, attachmentsByCipher.get(cipher.id) || [], { preserveRepairableUris, validFolderIds });
     if (isCipherResponseSyncCompatible(response)) {
       cipherResponses.push(response);
     }
diff --git a/src/services/storage-folder-repo.ts b/src/services/storage-folder-repo.ts
index 9e1701a..02c7660 100644
--- a/src/services/storage-folder-repo.ts
+++ b/src/services/storage-folder-repo.ts
@@ -44,9 +44,14 @@ export async function clearFolderFromCiphers(
       `UPDATE ciphers
        SET folder_id = NULL, updated_at = ?,
            data = json_remove(data, '$.folderId', '$.folder_id', '$.updatedAt', '$.revisionDate')
-       WHERE user_id = ? AND folder_id = ?`
+       WHERE user_id = ?
+         AND (
+           folder_id = ?
+           OR json_extract(data, '$.folderId') = ?
+           OR json_extract(data, '$.folder_id') = ?
+         )`
     )
-    .bind(now, userId, folderId)
+    .bind(now, userId, folderId, folderId, folderId)
     .run();
 }
 
@@ -71,9 +76,14 @@ export async function bulkDeleteFolders(
         `UPDATE ciphers
          SET folder_id = NULL, updated_at = ?,
              data = json_remove(data, '$.folderId', '$.folder_id', '$.updatedAt', '$.revisionDate')
-         WHERE user_id = ? AND folder_id IN (${placeholders})`
+         WHERE user_id = ?
+           AND (
+             folder_id IN (${placeholders})
+             OR json_extract(data, '$.folderId') IN (${placeholders})
+             OR json_extract(data, '$.folder_id') IN (${placeholders})
+           )`
       )
-      .bind(now, userId, ...chunk)
+      .bind(now, userId, ...chunk, ...chunk, ...chunk)
       .run();
 
     await db