diff --git a/readthedocs/projects/migrations/0030_change-max-length-project-slug.py b/readthedocs/projects/migrations/0030_change-max-length-project-slug.py
new file mode 100644
index 00000000000..a166a50fca6
--- /dev/null
+++ b/readthedocs/projects/migrations/0030_change-max-length-project-slug.py
@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.16 on 2018-11-01 20:55
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+from django.db.models.functions import Length
+
+
+def forwards_func(apps, schema_editor):
+    max_length = 63
+    Project = apps.get_model('projects', 'Project')
+    projects_invalid_slug = (
+        Project
+        .objects
+        .annotate(slug_length=Length('slug'))
+        .filter(slug_length__gt=max_length)
+    )
+    for project in projects_invalid_slug:
+        project.slug = project.slug[:max_length]
+        project.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('projects', '0029_add_additional_languages'),
+    ]
+
+    operations = [
+        migrations.RunPython(forwards_func),
+        migrations.AlterField(
+            model_name='project',
+            name='slug',
+            field=models.SlugField(max_length=63, unique=True, verbose_name='Slug'),
+        ),
+    ]
diff --git a/readthedocs/projects/models.py b/readthedocs/projects/models.py
index 9d5c3855f35..ca96ae1de3b 100644
--- a/readthedocs/projects/models.py
+++ b/readthedocs/projects/models.py
@@ -81,7 +81,8 @@ class Project(models.Model):
     users = models.ManyToManyField(User, verbose_name=_('User'),
                                    related_name='projects')
     name = models.CharField(_('Name'), max_length=255)
-    slug = models.SlugField(_('Slug'), max_length=255, unique=True)
+    # A DNS label can contain up to 63 characters.
+    slug = models.SlugField(_('Slug'), max_length=63, unique=True)
     description = models.TextField(_('Description'), blank=True,
                                    help_text=_('The reStructuredText '
                                                'description of the project'))