diff --git a/modules/purchase_trade/lot.py b/modules/purchase_trade/lot.py
index c1f54ef..83d1af8 100755
--- a/modules/purchase_trade/lot.py
+++ b/modules/purchase_trade/lot.py
@@ -1025,6 +1025,24 @@ class LotQt(
         logger.info("MATCH_LOTS:%s",lot_s)
         LotQt = Pool().get('lot.qt')
         Lot = Pool().get('lot.lot')
+        for lp in lot_p:
+            qt_p = Decimal(str(lp.lot_matched_qt or 0))
+            if qt_p <= 0:
+                continue
+            lqt = LotQt(lp.lot_r_id)
+            available = Decimal(str(lqt.lot_quantity or 0))
+            if qt_p > available:
+                raise UserError(
+                    "Quantity to match exceeds the available purchase quantity.")
+        for ls in lot_s:
+            qt_s = Decimal(str(ls.lot_matched_qt or 0))
+            if qt_s <= 0:
+                continue
+            lqt = LotQt(ls.lot_r_id)
+            available = abs(Decimal(str(lqt.lot_quantity or 0)))
+            if qt_s > available:
+                raise UserError(
+                    "Quantity to match exceeds the available sale quantity.")
         for lp in lot_p:
             qt_p = lp.lot_matched_qt
             if qt_p == 0:
diff --git a/modules/purchase_trade/service.py b/modules/purchase_trade/service.py
index 55348e3..abb373b 100644
--- a/modules/purchase_trade/service.py
+++ b/modules/purchase_trade/service.py
@@ -37,6 +37,7 @@ class ContractFactory:
 
         created = []
         sources = cls._get_sources(ct, type_)
+        cls._validate_requested_quantity(contracts, sources, ct)
         base_contract = cls._get_base_contract(sources, ct, type_)
 
         for c in contracts:
@@ -251,6 +252,18 @@ class ContractFactory:
             if getattr(line.unit, 'id', None) != getattr(first_line.unit, 'id', None):
                 raise UserError('Selected lots must share the same unit.')
 
+    @classmethod
+    def _validate_requested_quantity(cls, contracts, sources, ct):
+        if not getattr(ct, 'matched', False) or not sources:
+            return
+        available = sum(source['quantity'] for source in sources)
+        requested = sum(
+            cls._normalize_quantity(contract.quantity)
+            for contract in contracts)
+        if requested > available:
+            raise UserError(
+                'The requested quantity exceeds the selected open quantity.')
+
     @classmethod
     def _get_line_sources(cls, contract_detail, sources, ct):
         if not ct.matched or len(sources) <= 1:
diff --git a/modules/purchase_trade/tests/test_module.py b/modules/purchase_trade/tests/test_module.py
index 29c9652..b0431c9 100644
--- a/modules/purchase_trade/tests/test_module.py
+++ b/modules/purchase_trade/tests/test_module.py
@@ -2348,6 +2348,36 @@ class PurchaseTradeTestCase(ModuleTestCase):
         with self.assertRaises(UserError):
             ContractFactory._get_line_sources(contract_detail, sources, ct)
 
+    def test_contract_factory_rejects_total_above_selected_open_quantity(self):
+        'matched create contracts cannot consume more than selected open quantity'
+        contracts = [
+            Mock(quantity=Decimal('100')),
+            Mock(quantity=Decimal('100')),
+        ]
+        ct = Mock(matched=True)
+        sources = [
+            {'lot': Mock(), 'trade_line': Mock(), 'quantity': Decimal('100')},
+        ]
+
+        with self.assertRaises(UserError):
+            ContractFactory._validate_requested_quantity(contracts, sources, ct)
+
+    def test_lot_matching_rejects_purchase_quantity_above_available(self):
+        'apply matching cannot consume more than available purchase quantity'
+        class LotQtMock:
+            def __call__(self, _id):
+                return Mock(lot_quantity=Decimal('100'))
+
+        pool = Mock()
+        pool.get.side_effect = (
+            lambda name: LotQtMock() if name == 'lot.qt' else Mock())
+        purchase_lot = Mock(
+            lot_matched_qt=Decimal('101'), lot_r_id=1)
+
+        with patch.object(lot_module, 'Pool', return_value=pool):
+            with self.assertRaises(UserError):
+                lot_module.LotQt.match_lots([purchase_lot], [])
+
     def test_contract_detail_defaults_sale_locations_from_dropship_purchase(self):
         'create contracts copies supplier-to-customer locations from purchase to sale'
         supplier = Mock(id=1, type='supplier')