diff --git a/src/lib/validators/documents.ts b/src/lib/validators/documents.ts
index 02de6de8..dc9691f4 100644
--- a/src/lib/validators/documents.ts
+++ b/src/lib/validators/documents.ts
@@ -86,7 +86,11 @@ export const listDocumentsSchema = baseListQuerySchema
     interestId: z.string().optional(),
     clientId: z.string().optional(),
     documentType: z.string().optional(),
-    folderId: z.string().nullable().optional(),
+    folderId: z
+      .string()
+      .nullable()
+      .optional()
+      .transform((v) => (v === '' ? null : v)),
     includeDescendants: z.coerce.boolean().optional(),
     status: z.string().optional(),
     /** Hub tab filter - applies tab-specific status / signer-membership constraints. */
diff --git a/src/lib/validators/files.ts b/src/lib/validators/files.ts
index f74f7db5..096885c5 100644
--- a/src/lib/validators/files.ts
+++ b/src/lib/validators/files.ts
@@ -24,7 +24,11 @@ export const listFilesSchema = baseListQuerySchema
     yachtId: z.string().optional(),
     companyId: z.string().optional(),
     category: z.string().optional(),
-    folderId: z.string().uuid().optional(),
+    folderId: z
+      .string()
+      .uuid()
+      .optional()
+      .transform((v) => (v === '' ? null : v)),
     /** Entity-aggregated projection params — mutually exclusive with folderId. */
     entityType: z.enum(['client', 'company', 'yacht']).optional(),
     entityId: z.string().uuid().optional(),