diff --git a/CHANGELOG.md b/CHANGELOG.md
index 70f6e60..02b9979 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,14 @@ All notable changes to The Scheduler will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [Unreleased]
+
+### Fixed
+- `POST /tasks` returned HTTP 500 after successfully creating the task. The response
+  model declared `created_at`/`updated_at` as strings while the database returns
+  timestamps, so every create looked like a failure and retrying hit a duplicate-key
+  error.
+
 ## [1.1.3] - 2026-01-08
 
 ### Changed
diff --git a/src/models.py b/src/models.py
index f131b7f..a12a571 100644
--- a/src/models.py
+++ b/src/models.py
@@ -3,6 +3,7 @@ Pydantic models for The Scheduler API.
 """
 from pydantic import BaseModel, Field
 from typing import Optional, Dict, Any
+from datetime import datetime
 from enum import Enum
 
 
@@ -203,8 +204,13 @@ class TaskUpdate(BaseModel):
 
 class TaskResponse(TaskCreate):
     """Response model for task operations."""
-    created_at: str
-    updated_at: Optional[str] = None
+    # These are `timestamp` columns, so psycopg2 hands back datetime objects.
+    # Declaring them as `str` made Pydantic reject every create response, which
+    # 500'd the endpoint *after* the row had already been inserted and committed.
+    # FastAPI serialises datetime to an ISO 8601 string, so the JSON on the wire
+    # is unchanged — and now matches what GET /tasks/{name} already returned.
+    created_at: datetime
+    updated_at: Optional[datetime] = None
 
     class Config:
         from_attributes = True