diff --git a/chapeau/kepi/migrations/0002_acitem_serial.py b/chapeau/kepi/migrations/0002_acitem_serial.py
new file mode 100644
index 0000000..3b8c728
--- /dev/null
+++ b/chapeau/kepi/migrations/0002_acitem_serial.py
@@ -0,0 +1,18 @@
+# Generated by Django 2.2.4 on 2019-11-15 15:36
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('kepi', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='acitem',
+            name='serial',
+            field=models.IntegerField(default=0),
+        ),
+    ]
diff --git a/chapeau/kepi/models/item.py b/chapeau/kepi/models/item.py
index bf70753..950d7ba 100644
--- a/chapeau/kepi/models/item.py
+++ b/chapeau/kepi/models/item.py
@@ -3,6 +3,7 @@ from . import acobject, audience
 from .. import PUBLIC_IDS
 from django.conf import settings
 import logging
+import random
 
 logger = logging.getLogger(name='chapeau')
 
@@ -20,6 +21,32 @@ class AcItem(acobject.AcObject):
             blank=True,
             )
 
+    serial = models.IntegerField(
+            default = 0,
+            )
+
+    def _generate_id(self):
+        if not self.f_attributedTo:
+            logger.info('  -- new object has no f_attributedTo')
+            return super()._generate_id()
+
+        max_so_far = AcItem.objects.filter(
+                f_attributedTo = self.f_attributedTo,
+                ).aggregate(models.Max('serial'))['serial__max']
+
+        if max_so_far is None:
+            max_so_far = 0
+
+        self.serial = max_so_far + random.randint(0, 256)
+
+        logger.info('  -- max serial so far is %d; using serial %d',
+                max_so_far, self.serial)
+
+        # TODO: For now, we return the same IDs as the superclass.
+        # When I'm sure the serial numbers work and the tests pass,
+        # we'll have IDs in the form "/username/serial".
+        return super()._generate_id()
+
     @property
     def visibility(self):