diff --git a/apps/shipments/serializers.py b/apps/shipments/serializers.py
index 29de367..b49fe17 100644
--- a/apps/shipments/serializers.py
+++ b/apps/shipments/serializers.py
@@ -1,9 +1,35 @@
 from rest_framework import serializers
+
 from .models import Shipment
 
 
 class ShipmentSerializer(serializers.ModelSerializer):
+    """Mirror the ops form's rules, so the API cannot accept what the portal refuses.
+
+    The model tolerates a blank vessel or container and a missing date, because
+    records also arrive through this API. But a shipment is what the buyer's page
+    shows, so the fields the buyer reads are required here too, and a departure
+    after the arrival is refused. The bill of lading and the forwarder stay
+    optional; the ports keep their model defaults.
+    """
+
     class Meta:
         model = Shipment
         fields = "__all__"
         read_only_fields = ["id", "created_at"]
+        extra_kwargs = {
+            "status": {"required": True},
+            "vessel_name": {"required": True, "allow_blank": False},
+            "container_ref": {"required": True, "allow_blank": False},
+            "etd_nigeria": {"required": True, "allow_null": False},
+            "eta_uk": {"required": True, "allow_null": False},
+        }
+
+    def validate(self, attrs):
+        etd = attrs.get("etd_nigeria", getattr(self.instance, "etd_nigeria", None))
+        eta = attrs.get("eta_uk", getattr(self.instance, "eta_uk", None))
+        if etd and eta and etd > eta:
+            raise serializers.ValidationError(
+                {"eta_uk": "The ETA cannot be before the ETD. Check the two dates."}
+            )
+        return attrs