diff --git a/maigret/sites.py b/maigret/sites.py
index 62786997..0d8f0a1c 100644
--- a/maigret/sites.py
+++ b/maigret/sites.py
@@ -357,10 +357,10 @@ class MaigretSite:
         if not self.engine_obj:
             return self
 
-        self.request_future = None
-        self.url_regexp = None
-
-        self_copy = copy.deepcopy(self)
+        self_copy = copy.copy(self)
+        self_copy.request_future = None
+        self_copy.url_regexp = None
+        self_copy = copy.deepcopy(self_copy)
         engine_data = self_copy.engine_obj and self_copy.engine_obj.site or {}
         site_data_keys = list(self_copy.__dict__.keys())
 
diff --git a/tests/test_sites.py b/tests/test_sites.py
index be1a09c2..b4b96f54 100644
--- a/tests/test_sites.py
+++ b/tests/test_sites.py
@@ -119,6 +119,19 @@ def test_site_strip_engine_data():
     assert amperka_stripped.json == EXAMPLE_DB['sites']['Amperka']
 
 
+def test_saving_database_preserves_site_url_detector(tmp_path):
+    db = MaigretDatabase()
+    db.load_from_json(EXAMPLE_DB)
+    amperka = db.sites[0]
+
+    db.save_to_file(str(tmp_path / 'data.json'))
+
+    assert (
+        amperka.detect_username('http://forum.amperka.ru/members/?username=test')
+        == 'test'
+    )
+
+
 def test_site_strip_engine_data_with_site_prior_updates():
     db = MaigretDatabase()
     UPDATED_EXAMPLE_DB = dict(EXAMPLE_DB)