diff --git a/src/applications/config/check/PhabricatorSetupCheckBaseURI.php b/src/applications/config/check/PhabricatorSetupCheckBaseURI.php
index 34bcfb9599..1a5671a737 100644
--- a/src/applications/config/check/PhabricatorSetupCheckBaseURI.php
+++ b/src/applications/config/check/PhabricatorSetupCheckBaseURI.php
@@ -4,6 +4,26 @@ final class PhabricatorSetupCheckBaseURI extends PhabricatorSetupCheck {
 
   protected function executeChecks() {
     $base_uri = PhabricatorEnv::getEnvConfig('phabricator.base-uri');
+
+    if (strpos($_SERVER['HTTP_HOST'], '.') === false) {
+      $summary = pht(
+        'The domain does not contain a dot. This is necessary for some web '.
+        'browsers to be able to set cookies.');
+
+      $message = pht(
+        'The domain in the base URI must contain a dot ("."), e.g. '.
+        '"http://example.com", not just a bare name like "http://example/". '.
+        'Some web browsers will not set cookies on domains with no TLD.');
+
+      $this
+        ->newIssue('config.phabricator.domain')
+        ->setShortName(pht('Dotless Domain'))
+        ->setName(pht('No Dot Character in Domain'))
+        ->setSummary($summary)
+        ->setMessage($message)
+        ->setIsFatal(true);
+    }
+
     if ($base_uri) {
       return;
     }
diff --git a/src/docs/configuration/configuration_guide.diviner b/src/docs/configuration/configuration_guide.diviner
index e8a2e5765b..b5e2c5c69d 100644
--- a/src/docs/configuration/configuration_guide.diviner
+++ b/src/docs/configuration/configuration_guide.diviner
@@ -30,6 +30,9 @@ some subdirectory of an existing website. Navigate to whatever domain you're
 going to use and make sure Apache serves you something to verify that DNS
 is correctly configured.
 
+NOTE: The domain must contain a dot ('.'), i.e. not be just a bare name like
+'http://example/'. Some web browsers will not set cookies otherwise.
+
 Now, either create a VirtualHost entry (to put Phabricator on a subdomain)
 or edit the Directory entry for the DocumentRoot. It should look something like
 this: