diff --git a/scripts/sync_catalog.py b/scripts/sync_catalog.py
index f1bf1d3..02ad523 100755
--- a/scripts/sync_catalog.py
+++ b/scripts/sync_catalog.py
@@ -24,6 +24,7 @@
 from typing import Any
 
 DEFAULT_SOURCE = "https://plugins.aiuo.net/catalog.json"
+DEFAULT_ARTIFACT_BASE = "https://raw.githubusercontent.com/vastsa/pi-desktop-plugins/main"
 UA = "pi-desktop-plugins-mirror/1.0"
 MAX_PACKAGE_BYTES = 50 * 1024 * 1024
 CATALOG_TIMEOUT = 30
@@ -89,9 +90,9 @@ def resolve_download_url(catalog: dict[str, Any], rel: str) -> str:
     return base + rel.lstrip("/")
 
 
-def rewrite_for_mirror(src: dict[str, Any]) -> dict[str, Any]:
+def rewrite_for_mirror(src: dict[str, Any], artifact_base: str = DEFAULT_ARTIFACT_BASE) -> dict[str, Any]:
     out = copy.deepcopy(src)
-    out.pop("artifactBaseUrl", None)
+    out["artifactBaseUrl"] = artifact_base
     out.pop("artifactBaseURL", None)
     for p in out.get("plugins") or []:
         pid = p.get("id")
@@ -139,10 +140,11 @@ def sync(root: Path, source: str, dry_run: bool) -> int:
         raise SystemExit(f"catalog is not JSON: {e}") from e
     validate_catalog(src)
 
-    mirrored = rewrite_for_mirror(src)
+    existing = load_json(root / "catalog.json")
+    artifact_base = ((existing or {}).get("artifactBaseUrl") or (existing or {}).get("artifactBaseURL") or "").strip()
+    mirrored = rewrite_for_mirror(src, artifact_base or DEFAULT_ARTIFACT_BASE)
     validate_catalog(mirrored)
 
-    existing = load_json(root / "catalog.json")
     if existing and canonical(existing) == canonical(mirrored):
         print("catalog unchanged (ignoring generatedAt/catalogId/updatedAt)")
         return 0
diff --git a/tests/test_sync_catalog.py b/tests/test_sync_catalog.py
index c03e3ba..bb1b3b0 100644
--- a/tests/test_sync_catalog.py
+++ b/tests/test_sync_catalog.py
@@ -9,6 +9,7 @@
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 from pathlib import Path
 from threading import Thread
+from unittest.mock import patch
 
 ROOT = Path(__file__).resolve().parents[1]
 SCRIPTS = ROOT / "scripts"
@@ -26,7 +27,7 @@ def load_sync():
 
 
 class RewriteTests(unittest.TestCase):
-    def test_rewrite_drops_artifact_base_and_uses_packages(self):
+    def test_rewrite_declares_mirror_artifact_base_and_uses_packages(self):
         src = {
             "schemaVersion": 2,
             "providerId": "official",
@@ -45,10 +46,18 @@ def test_rewrite_drops_artifact_base_and_uses_packages(self):
             ],
         }
         out = sync.rewrite_for_mirror(src)
-        self.assertNotIn("artifactBaseUrl", out)
+        self.assertEqual(out["artifactBaseUrl"], "https://raw.githubusercontent.com/vastsa/pi-desktop-plugins/main")
+        self.assertEqual(src["artifactBaseUrl"], "https://plugins.aiuo.net/api/pi/v1/")
         self.assertEqual(out["plugins"][0]["versions"][0]["url"], "packages/demo.hello-1.0.0.piplug")
         self.assertEqual(src["plugins"][0]["versions"][0]["url"], "plugins/demo.hello/versions/1.0.0/artifact")
 
+    def test_rewrite_uses_selected_mirror_base_not_source_alias(self):
+        src = {"artifactBaseURL": "https://center.example/artifacts/", "plugins": []}
+        out = sync.rewrite_for_mirror(src, "https://mirror.example/plugins/")
+        self.assertEqual(out["artifactBaseUrl"], "https://mirror.example/plugins/")
+        self.assertNotIn("artifactBaseURL", out)
+        self.assertEqual(src["artifactBaseURL"], "https://center.example/artifacts/")
+
     def test_empty_catalog_rejected(self):
         with self.assertRaises(SystemExit):
             sync.validate_catalog({"providerId": "official", "plugins": []})
@@ -121,7 +130,7 @@ def log_message(self, format, *args):
                 self.assertEqual(rc, 0)
                 new = json.loads((root / "catalog.json").read_text(encoding="utf-8"))
                 self.assertEqual(new["plugins"][0]["id"], "demo.hello")
-                self.assertNotIn("artifactBaseUrl", new)
+                self.assertEqual(new["artifactBaseUrl"], "https://raw.githubusercontent.com/vastsa/pi-desktop-plugins/main")
                 pkg = root / "packages" / "demo.hello-1.0.0.piplug"
                 self.assertTrue(pkg.exists())
                 self.assertEqual(pkg.read_bytes(), blob)
@@ -140,6 +149,28 @@ def test_http_error_leaves_catalog(self):
                 sync.sync(root, "http://127.0.0.1:1/catalog.json", dry_run=False)
             self.assertEqual((root / "catalog.json").read_text(encoding="utf-8"), old)
 
+    def test_sync_keeps_existing_mirror_base(self):
+        blob = b"hello-piplug"
+        src = {
+            "providerId": "official",
+            "artifactBaseUrl": "https://center.example/artifacts/",
+            "plugins": [{"id": "demo.hello", "versions": [{
+                "version": "1.0.0", "shasum": sync.sha256_bytes(blob), "url": "hello.piplug",
+            }]}],
+        }
+        for key in ("artifactBaseUrl", "artifactBaseURL"):
+            with self.subTest(key=key), tempfile.TemporaryDirectory() as tmp:
+                root = Path(tmp)
+                old = {"providerId": "official", key: "https://mirror.example/releases/", "plugins": []}
+                (root / "catalog.json").write_text(json.dumps(old), encoding="utf-8")
+                with patch.object(sync, "fetch", side_effect=[json.dumps(src).encode(), blob, b"signature"]) as fetch:
+                    self.assertEqual(sync.sync(root, "https://center.example/catalog.json", False), 0)
+                new = json.loads((root / "catalog.json").read_text(encoding="utf-8"))
+                self.assertEqual(new["artifactBaseUrl"], "https://mirror.example/releases/")
+                self.assertNotIn("artifactBaseURL", new)
+                self.assertEqual(new["plugins"][0]["versions"][0]["url"], "packages/demo.hello-1.0.0.piplug")
+                self.assertEqual(fetch.call_args_list[1].args[0], "https://center.example/artifacts/hello.piplug")
+
 
 if __name__ == "__main__":
     sys.exit(unittest.main())