diff --git a/fusion_clock/__manifest__.py b/fusion_clock/__manifest__.py
index 0ffbfc64..77de44f8 100644
--- a/fusion_clock/__manifest__.py
+++ b/fusion_clock/__manifest__.py
@@ -5,7 +5,7 @@
 
 {
     'name': 'Fusion Clock',
-    'version': '19.0.3.12.2',
+    'version': '19.0.3.12.3',
     'category': 'Human Resources/Attendances',
     'summary': 'Complete Employee T&A with Geofencing, Shifts, Penalties, Overtime, Kiosk, Dashboard & Payroll Export',
     'description': """
diff --git a/fusion_clock/models/hr_employee.py b/fusion_clock/models/hr_employee.py
index 0b55524f..f8a73e0e 100644
--- a/fusion_clock/models/hr_employee.py
+++ b/fusion_clock/models/hr_employee.py
@@ -58,13 +58,15 @@ class HrEmployee(models.Model):
              "Same card the employee uses for door access.",
     )
 
-    _sql_constraints = [
-        (
-            'fclk_nfc_card_uid_unique',
-            'UNIQUE(x_fclk_nfc_card_uid)',
-            'This NFC card is already assigned to another employee.',
-        ),
-    ]
+    # Enforce NFC card-UID uniqueness ONLY when a UID is set. Odoo 19 silently ignores
+    # the legacy `_sql_constraints` list (see repo-root CLAUDE.md rule 9), so this never
+    # created a DB constraint. Use the declarative UniqueIndex with a partial WHERE so the
+    # many employees without a card can share a blank/NULL value, while two employees can
+    # never be assigned the same physical card.
+    _fclk_nfc_card_uid_unique = models.UniqueIndex(
+        "(x_fclk_nfc_card_uid) WHERE x_fclk_nfc_card_uid IS NOT NULL AND x_fclk_nfc_card_uid != ''",
+        'This NFC card is already assigned to another employee.',
+    )
 
     # On-time streak
     x_fclk_ontime_streak = fields.Integer(