diff --git a/Web/modules/database/user.py b/Web/modules/database/user.py
index 1bd4ff7..4dc7a10 100755
--- a/Web/modules/database/user.py
+++ b/Web/modules/database/user.py
@@ -54,10 +54,34 @@ def _clean_name_fragment(value):
     return cleaned
 
 
-def _get_tenant_db(client):
+def _get_tenant_db(client, tenant_id=None):
     """Return the current tenant database for the request, or fall back to default."""
     try:
         from tenant import get_tenant_db
+        if tenant_id is None:
+            return get_tenant_db(client)
+
+        tenant_id = str(tenant_id).strip()
+        if tenant_id:
+            try:
+                from tenant import get_tenant_config
+
+                config = get_tenant_config(tenant_id)
+                if isinstance(config, dict):
+                    explicit_db = config.get('db') or config.get('db_name')
+                    if explicit_db:
+                        db_name = str(explicit_db).strip()
+                        if db_name and not db_name.startswith('inventar_'):
+                            db_name = f'inventar_{db_name}'
+                        if db_name:
+                            return client[db_name]
+            except Exception:
+                pass
+
+            sanitized = ''.join(c for c in tenant_id.lower() if c.isalnum() or c == '_')
+            if sanitized:
+                return client[f'inventar_{sanitized}']
+
         return get_tenant_db(client)
     except Exception:
         return client[cfg.MONGODB_DB]
@@ -479,8 +503,45 @@ def check_nm_pwd(username, password):
             query = {'$or': [{'Username': username}, {'username': username}]}
             user_record_fallback = users.find_one(query)
             if user_record_fallback is None:
-                logger.warning("Kein Benutzer für %r in DB %r gefunden.", dp.encrypt_text(username), db_name)
-                return None
+                if db_name != cfg.MONGODB_DB:
+                    default_users = client[cfg.MONGODB_DB]['users']
+                    user_record_fallback = default_users.find_one(
+                        {'$or': [
+                            {'Username': dp.encrypt_text(username)},
+                            {'username': dp.encrypt_text(username)},
+                            {'Username': username},
+                            {'username': username},
+                        ]}
+                    )
+                    if user_record_fallback is not None:
+                        migrated_record = dict(user_record_fallback)
+                        migrated_record.pop('_id', None)
+                        users.replace_one(
+                            {'$or': [
+                                {'Username': migrated_record.get('Username')},
+                                {'username': migrated_record.get('username')},
+                            ]},
+                            migrated_record,
+                            upsert=True,
+                        )
+                        logger.warning(
+                            "Tenant user %r migrated from default DB %r to tenant DB %r.",
+                            dp.encrypt_text(username),
+                            cfg.MONGODB_DB,
+                            db_name,
+                        )
+                        user_record = users.find_one(
+                            {'$or': [
+                                {'Username': migrated_record.get('Username')},
+                                {'username': migrated_record.get('username')},
+                            ]}
+                        ) or migrated_record
+                    else:
+                        logger.warning("Kein Benutzer für %r in DB %r gefunden.", dp.encrypt_text(username), db_name)
+                        return None
+                else:
+                    logger.warning("Kein Benutzer für %r in DB %r gefunden.", dp.encrypt_text(username), db_name)
+                    return None
             else:
                 user_record = user_record_fallback
 
@@ -506,6 +567,7 @@ def add_admin(
     permission_preset='full_access',
     action_permissions=None,
     page_permissions=None,
+    tenant_id=None,
 ):
     """
     Add a new user to the database.
@@ -515,7 +577,7 @@ def add_admin(
 
     client = MongoClient(cfg.MONGODB_HOST, cfg.MONGODB_PORT)
     try:
-        db = _get_tenant_db(client)
+        db = _get_tenant_db(client, tenant_id)
         users = db['users']
 
         permission_defaults = build_default_permission_payload(permission_preset)
@@ -561,6 +623,7 @@ def add_user(
     permission_preset='standard_user',
     action_permissions=None,
     page_permissions=None,
+    tenant_id=None,
 ):
     """
     Add a new user to the database.
@@ -570,7 +633,7 @@ def add_user(
 
     client = MongoClient(cfg.MONGODB_HOST, cfg.MONGODB_PORT)
     try:
-        db = _get_tenant_db(client)
+        db = _get_tenant_db(client, tenant_id)
         users = db['users']
 
         permission_defaults = build_default_permission_payload(permission_preset)
diff --git a/manage-tenant.sh b/manage-tenant.sh
index a4bd320..b59ba5b 100755
--- a/manage-tenant.sh
+++ b/manage-tenant.sh
@@ -206,12 +206,30 @@ import Web.modules.database.user as us
 tenant_id = sys.argv[1].lower()
 mode = sys.argv[2]
 sanitized = "".join(c for c in tenant_id if c.isalnum() or c == "_")
+db_name = f"inventar_{sanitized}" if sanitized else settings.MONGODB_DB
 
-us.add_admin("admin", "admin123", "admin", "admin")
-us.make_admin("admin")
+client = MongoClient(settings.MONGODB_HOST, settings.MONGODB_PORT)
+db = client[db_name]
+users = db["users"]
+permission_defaults = us.build_default_permission_payload("full_access")
+admin_doc = {
+    "Username": "admin",
+    "Password": us.hashing("admin123"),
+    "Admin": True,
+    "active_ausleihung": None,
+    "name": dp.encrypt_text("admin"),
+    "last_name": dp.encrypt_text("admin"),
+    "IsStudent": False,
+    "PermissionPreset": permission_defaults["preset"],
+    "ActionPermissions": permission_defaults["actions"],
+    "PagePermissions": permission_defaults["pages"],
+}
+users.replace_one({"Username": "admin"}, admin_doc, upsert=True)
 print("Fallback successfully applied")
 
 if mode == "trial":
+    client = MongoClient(settings.MONGODB_HOST, settings.MONGODB_PORT)
+    db = client[db_name]
     db.settings.update_one(
         {"setting_type": "tenant_trial"},
         {"$set": {
@@ -224,6 +242,8 @@ if mode == "trial":
         upsert=True,
     )
 
+client.close()
+
 print(f"Tenant {sys.argv[1]} database initialized. Default admin: admin / admin123")
 PY
 }