diff --git a/B01_Dashboard/B01_Dashboard_Repository.py b/B01_Dashboard/B01_Dashboard_Repository.py
index 9a3976f3..25fee587 100644
--- a/B01_Dashboard/B01_Dashboard_Repository.py
+++ b/B01_Dashboard/B01_Dashboard_Repository.py
@@ -287,7 +287,14 @@ async def update_project(project_id: str, data: dict[str, Any], actor_id: int) -
             ),
         )
         changed = cursor.rowcount > 0
-        if changed:
+        if not changed:
+            # 값이 하나도 안 바뀌면 rowcount 가 0 이다 — 프로젝트가 없는 것과는 다르다
+            # (참여자만 바꿀 때 「찾을 수 없습니다」로 튕기던 자리, 2026-09-06).
+            await cursor.execute(
+                "SELECT 1 FROM projects WHERE id = %s AND deleted_at IS NULL", (project_id,)
+            )
+            changed = await cursor.fetchone() is not None
+        else:
             await cursor.execute(
                 """INSERT INTO system_audit_logs (user_id, action, resource_type, resource_id)
                    VALUES (%s, 'PROJECT_UPDATE', 'project', NULL)""",