diff --git a/InvenTree/order/migrations/0053_salesordershipment.py b/InvenTree/order/migrations/0053_salesordershipment.py
index e20a95e3f8..b137e2dea8 100644
--- a/InvenTree/order/migrations/0053_salesordershipment.py
+++ b/InvenTree/order/migrations/0053_salesordershipment.py
@@ -3,6 +3,9 @@
 from django.conf import settings
 from django.db import migrations, models
 import django.db.models.deletion
+
+import order.models
+
 import markdownx.models
 
 
@@ -19,7 +22,7 @@ class Migration(migrations.Migration):
             fields=[
                 ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                 ('shipment_date', models.DateField(blank=True, help_text='Date of shipment', null=True, verbose_name='Shipment Date')),
-                ('reference', models.CharField(blank=True, help_text='Shipment reference', max_length=100, verbose_name='Reference')),
+                ('reference', models.CharField(default=order.models.get_next_shipment_number, unique=True, help_text='Shipment reference', max_length=100, verbose_name='Reference')),
                 ('notes', markdownx.models.MarkdownxField(blank=True, help_text='Shipment notes', verbose_name='Notes')),
                 ('checked_by', models.ForeignKey(blank=True, help_text='User who checked this shipment', null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='+', to=settings.AUTH_USER_MODEL, verbose_name='Checked By')),
                 ('order', models.ForeignKey(help_text='Sales Order', on_delete=django.db.models.deletion.CASCADE, related_name='shipments', to='order.salesorder', verbose_name='Order')),
diff --git a/InvenTree/order/models.py b/InvenTree/order/models.py
index c6ff6dc5bd..b0b0d82221 100644
--- a/InvenTree/order/models.py
+++ b/InvenTree/order/models.py
@@ -37,7 +37,7 @@ def get_next_po_number():
     """
 
     if PurchaseOrder.objects.count() == 0:
-        return
+        return "001"
 
     order = PurchaseOrder.objects.exclude(reference=None).last()
 
@@ -66,7 +66,7 @@ def get_next_so_number():
     """
 
     if SalesOrder.objects.count() == 0:
-        return
+        return "001"
 
     order = SalesOrder.objects.exclude(reference=None).last()
 
@@ -107,45 +107,6 @@ class Order(ReferenceIndexingMixin):
         responsible: User (or group) responsible for managing the order
     """
 
-    @classmethod
-    def getNextOrderNumber(cls):
-        """
-        Try to predict the next order-number
-        """
-
-        if cls.objects.count() == 0:
-            return None
-
-        # We will assume that the latest pk has the highest PO number
-        order = cls.objects.last()
-        ref = order.reference
-
-        if not ref:
-            return None
-
-        tries = set()
-
-        tries.add(ref)
-
-        while 1:
-            new_ref = increment(ref)
-
-            print("Reference:", new_ref)
-
-            if new_ref in tries:
-                # We are in a looping situation - simply return the original one
-                return ref
-
-            # Check that the new ref does not exist in the database
-            if cls.objects.filter(reference=new_ref).exists():
-                tries.add(new_ref)
-                new_ref = increment(new_ref)
-
-            else:
-                break
-
-        return new_ref
-
     def save(self, *args, **kwargs):
 
         self.rebuild_reference_field()
@@ -903,6 +864,35 @@ class SalesOrderLineItem(OrderLineItem):
         return self.allocated_quantity() > self.quantity
 
 
+def get_next_shipment_number():
+    """
+    Returns the next available SalesOrderShipment reference number"
+    """
+
+    if SalesOrderShipment.objects.count() == 0:
+        return "001"
+
+    shipment = SalesOrderShipment.objects.exclude(reference=None).last()
+
+    attempts = set([shipment.reference])
+
+    reference = shipment.reference
+
+    while 1:
+        reference = increment(reference)
+
+        if reference in attempts:
+            # Escape infinite recursion
+            return reference
+
+        if SalesOrderShipment.objects.filter(reference=reference).exists():
+            attempts.add(reference)
+        else:
+            break
+
+    return reference
+
+
 class SalesOrderShipment(models.Model):
     """
     The SalesOrderShipment model represents a physical shipment made against a SalesOrder.
@@ -946,9 +936,11 @@ class SalesOrderShipment(models.Model):
 
     reference = models.CharField(
         max_length=100,
-        blank=True,
+        blank=False,
+        unique=True,
         verbose_name=('Reference'),
         help_text=_('Shipment reference'),
+        default=get_next_shipment_number,
     )
 
     notes = MarkdownxField(