diff --git a/shipment.py b/shipment.py
index dac83f5..05895b7 100644
--- a/shipment.py
+++ b/shipment.py
@@ -241,6 +241,13 @@ class ShipmentIn(EdifactMixin, metaclass=PoolMeta):
                 ('number', '=', purchase_num),
                 ('state', 'in', ('processing', 'done'))
                 ], limit=1) or [None]
+        if not purchase:
+            purchases = Purchase.search([
+                    ('reference', '=', purchase_num),
+                    ('state', 'in', ('processing', 'done'))
+                    ])
+            if len(purchases) == 1:
+                purchase = purchase[0]
         if not purchase:
             error_msg = 'Purchase number {} not found'.format(purchase_num)
             serialized_segment = Serializer(control_chars).serialize([segment])