diff --git a/kobo/django/upload/migrations/0002_alter_fileupload_size.py b/kobo/django/upload/migrations/0002_alter_fileupload_size.py
new file mode 100644
index 00000000..f5648eee
--- /dev/null
+++ b/kobo/django/upload/migrations/0002_alter_fileupload_size.py
@@ -0,0 +1,19 @@
+# Generated by Django 3.2.20 on 2023-08-22 09:45
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('upload', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='fileupload',
+            name='size',
+            field=models.BigIntegerField(validators=[django.core.validators.MinValueValidator(0)]),
+        ),
+    ]
diff --git a/kobo/django/upload/models.py b/kobo/django/upload/models.py
index f5f23b2f..68d65c6f 100644
--- a/kobo/django/upload/models.py
+++ b/kobo/django/upload/models.py
@@ -4,6 +4,7 @@
 import os
 
 from django.conf import settings
+from django.core.validators import MinValueValidator
 from django.db import models
 from django.contrib.auth.models import User
 
@@ -25,7 +26,8 @@ class FileUpload(models.Model):
     owner       = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
     name        = models.CharField(max_length=255)
     checksum    = models.CharField(max_length=255)
-    size        = models.PositiveIntegerField()
+    # models.PositiveBigIntegerField would be even better but it was introduced only in Django 3.1
+    size        = models.BigIntegerField(validators=[MinValueValidator(0)])
     target_dir = models.CharField(max_length=255)
     upload_key  = models.CharField(max_length=255)
     state       = models.PositiveIntegerField(default=0, choices=UPLOAD_STATES.get_mapping())
@@ -66,6 +68,9 @@ def save(self, *args, **kwargs):
                 self.state = UPLOAD_STATES['FAILED']
                 if "update_fields" in kwargs:
                     kwargs["update_fields"] = {"state"}.union(kwargs["update_fields"])
+
+        # execute validators
+        self.full_clean()
         super(FileUpload, self).save(*args, **kwargs)
 
     def delete(self):