diff --git a/src/aphront/site/PhabricatorPlatformSite.php b/src/aphront/site/PhabricatorPlatformSite.php
index 21e2cd2529..63c2b9cde3 100644
--- a/src/aphront/site/PhabricatorPlatformSite.php
+++ b/src/aphront/site/PhabricatorPlatformSite.php
@@ -1,33 +1,40 @@
 <?php
 
 final class PhabricatorPlatformSite extends PhabricatorSite {
 
   public function getDescription() {
     return pht('Serves the core platform and applications.');
   }
 
   public function getPriority() {
     return 1000;
   }
 
   public function newSiteForRequest(AphrontRequest $request) {
+    // If no base URI has been configured yet, match this site so the user
+    // can follow setup instructions.
+    $base_uri = PhabricatorEnv::getEnvConfig('phabricator.base-uri');
+    if (!strlen($base_uri)) {
+      return new PhabricatorPlatformSite();
+    }
+
     $uris = array();
-    $uris[] = PhabricatorEnv::getEnvConfig('phabricator.base-uri');
+    $uris[] = $base_uri;
     $uris[] = PhabricatorEnv::getEnvConfig('phabricator.production-uri');
 
     $allowed = PhabricatorEnv::getEnvConfig('phabricator.allowed-uris');
     if ($allowed) {
       foreach ($allowed as $uri) {
         $uris[] = $uri;
       }
     }
 
     $host = $request->getHost();
     if ($this->isHostMatch($host, $uris)) {
       return new PhabricatorPlatformSite();
     }
 
     return null;
   }
 
 }