diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index b4a10a4d30..17cd716b52 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -2300,6 +2300,12 @@ def bulk_add_subscriptions(streams: Iterable[Stream],
     # Log Subscription Activities in RealmAuditLog
     event_time = timezone_now()
     event_last_message_id = Message.objects.aggregate(Max('id'))['id__max']
+    if event_last_message_id is None:
+        # During initial realm creation, there might be 0 messages in
+        # the database; in that case, the `aggregate` query returns
+        # None.  Since we want an int for "beginning of time", use -1.
+        event_last_message_id = -1
+
     all_subscription_logs = []  # type: (List[RealmAuditLog])
     for (sub, stream) in subs_to_add:
         all_subscription_logs.append(RealmAuditLog(realm=sub.user_profile.realm,
diff --git a/zerver/migrations/0139_fill_last_message_id_in_subscription_logs.py b/zerver/migrations/0139_fill_last_message_id_in_subscription_logs.py
new file mode 100644
index 0000000000..0fae9f9933
--- /dev/null
+++ b/zerver/migrations/0139_fill_last_message_id_in_subscription_logs.py
@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+from django.db.backends.postgresql_psycopg2.schema import DatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+
+def backfill_last_message_id(apps: StateApps, schema_editor: DatabaseSchemaEditor) -> None:
+    event_type = ['subscription_created', 'subscription_deactivated', 'subscription_activated']
+    RealmAuditLog = apps.get_model('zerver', 'RealmAuditLog')
+    subscription_logs = RealmAuditLog.objects.filter(
+        event_last_message_id__isnull=True, event_type__in=event_type)
+    subscription_logs.update(event_last_message_id=-1)
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('zerver', '0138_userprofile_realm_name_in_notifications'),
+    ]
+
+    operations = [
+        migrations.RunPython(backfill_last_message_id,
+                             reverse_code=migrations.RunPython.noop),
+    ]