diff --git a/src/claude_memory/api/app.py b/src/claude_memory/api/app.py
index a263fd8..756084b 100644
--- a/src/claude_memory/api/app.py
+++ b/src/claude_memory/api/app.py
@@ -69,16 +69,17 @@ async def sync_memories(
 
     async with pool.acquire() as conn:
         if since:
+            since_dt = datetime.fromisoformat(since)
             rows = await conn.fetch(
                 """
                 SELECT id, content, category, tags, expanded_keywords, importance,
                        is_sensitive, created_at, updated_at, deleted_at
                 FROM memories
-                WHERE user_id = $1 AND updated_at > $2::timestamptz
+                WHERE user_id = $1 AND updated_at > $2
                 ORDER BY updated_at ASC
                 """,
                 user.user_id,
-                since,
+                since_dt,
             )
         else:
             rows = await conn.fetch(
diff --git a/tests/test_api.py b/tests/test_api.py
index 88ecfc6..60d4b1f 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -349,7 +349,7 @@ async def test_sync_incremental_with_since(client):
 
     async with ac:
         resp = await ac.get(
-            "/api/memories/sync?since=2026-03-14T10:00:00+00:00",
+            "/api/memories/sync?since=2026-03-14T10:00:00Z",
             headers={"Authorization": "Bearer test-key"},
         )
 
@@ -374,7 +374,7 @@ async def test_sync_includes_soft_deleted_with_since(client):
 
     async with ac:
         resp = await ac.get(
-            "/api/memories/sync?since=2026-03-14T10:00:00+00:00",
+            "/api/memories/sync?since=2026-03-14T10:00:00Z",
             headers={"Authorization": "Bearer test-key"},
         )