diff --git a/backend/src/db.ts b/backend/src/db.ts
index a236eb0..bfbfe69 100644
--- a/backend/src/db.ts
+++ b/backend/src/db.ts
@@ -15,7 +15,7 @@ const poolConfig: PoolConfig = {
 
 function mockRowFromInsert(sql: string, params: unknown[]): RaceRow {
   const match = sql.match(/INSERT INTO races\s*\(([^)]+)\)\s*VALUES/i);
-  const now = new Date().toISOString();
+  const now = new Date();
   if (!match) {
     return {
       id: String(params[0] ?? ""),
@@ -108,7 +108,7 @@ function createMockPool(): Pool {
       if (!existing) {
         return emptyResult();
       }
-      const updated = { ...existing, updated_at: new Date().toISOString() };
+      const updated = { ...existing, updated_at: new Date() };
       store.set(id, updated);
       return {
         rows: [updated as unknown as T],
diff --git a/backend/src/mappers/race.ts b/backend/src/mappers/race.ts
index a1c22d5..cf83194 100644
--- a/backend/src/mappers/race.ts
+++ b/backend/src/mappers/race.ts
@@ -1,4 +1,7 @@
-/** Row shape returned by PostgreSQL (snake_case). */
+/**
+ * Row shape returned by PostgreSQL (snake_case).
+ * pg returns DATE as string, NUMERIC as string, TIMESTAMPTZ as Date.
+ */
 export interface RaceRow {
   id: string;
   race_date: string;
@@ -13,8 +16,8 @@ export interface RaceRow {
   finish_time: string | null;
   finish_place: string | null;
   notes: string | null;
-  created_at: string;
-  updated_at: string | null;
+  created_at: Date;
+  updated_at: Date | null;
 }
 
 /** API shape (camelCase). */
@@ -36,6 +39,10 @@ export interface RaceDto {
   updatedAt: string | null;
 }
 
+function toISOString(value: Date | string): string {
+  return value instanceof Date ? value.toISOString() : String(value);
+}
+
 /** Convert a DB row to the API DTO (camelCase). */
 export function rowToDto(row: RaceRow): RaceDto {
   return {
@@ -52,8 +59,8 @@ export function rowToDto(row: RaceRow): RaceDto {
     finishTime: row.finish_time,
     finishPlace: row.finish_place,
     notes: row.notes,
-    createdAt: row.created_at,
-    updatedAt: row.updated_at,
+    createdAt: toISOString(row.created_at),
+    updatedAt: row.updated_at ? toISOString(row.updated_at) : null,
   };
 }
 
diff --git a/frontend/src/features/index.ts b/frontend/src/features/index.ts
deleted file mode 100644
index cb0ff5c..0000000
--- a/frontend/src/features/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export {};