diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index aa77f1121a..cca5e4fc2b 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1455,6 +1455,7 @@ phutil_register_library_map(array(
     'PhabricatorConfigSchemaQuery' => 'applications/config/schema/PhabricatorConfigSchemaQuery.php',
     'PhabricatorConfigSchemaSpec' => 'applications/config/schema/PhabricatorConfigSchemaSpec.php',
     'PhabricatorConfigServerSchema' => 'applications/config/schema/PhabricatorConfigServerSchema.php',
+    'PhabricatorConfigSiteSource' => 'infrastructure/env/PhabricatorConfigSiteSource.php',
     'PhabricatorConfigSource' => 'infrastructure/env/PhabricatorConfigSource.php',
     'PhabricatorConfigStackSource' => 'infrastructure/env/PhabricatorConfigStackSource.php',
     'PhabricatorConfigStorageSchema' => 'applications/config/schema/PhabricatorConfigStorageSchema.php',
@@ -4534,6 +4535,7 @@ phutil_register_library_map(array(
     'PhabricatorConfigSchemaQuery' => 'Phobject',
     'PhabricatorConfigSchemaSpec' => 'Phobject',
     'PhabricatorConfigServerSchema' => 'PhabricatorConfigStorageSchema',
+    'PhabricatorConfigSiteSource' => 'PhabricatorConfigProxySource',
     'PhabricatorConfigStackSource' => 'PhabricatorConfigSource',
     'PhabricatorConfigStorageSchema' => 'Phobject',
     'PhabricatorConfigTableSchema' => 'PhabricatorConfigStorageSchema',
diff --git a/src/infrastructure/env/PhabricatorConfigSiteSource.php b/src/infrastructure/env/PhabricatorConfigSiteSource.php
new file mode 100644
index 0000000000..fdec619c9d
--- /dev/null
+++ b/src/infrastructure/env/PhabricatorConfigSiteSource.php
@@ -0,0 +1,17 @@
+<?php
+
+/**
+ * Optional configuration source which loads between local sources and the
+ * database source.
+ *
+ * Subclasses of this source can read external configuration sources (like a
+ * remote server).
+ */
+abstract class PhabricatorConfigSiteSource
+  extends PhabricatorConfigProxySource {
+
+  public function getPriority() {
+    return 1000.0;
+  }
+
+}
diff --git a/src/infrastructure/env/PhabricatorEnv.php b/src/infrastructure/env/PhabricatorEnv.php
index 78ab762ea6..5d1a65a7df 100644
--- a/src/infrastructure/env/PhabricatorEnv.php
+++ b/src/infrastructure/env/PhabricatorEnv.php
@@ -153,6 +153,15 @@ final class PhabricatorEnv {
     // pull in all options from non-phabricator libraries now they are loaded.
     $default_source->loadExternalOptions();
 
+    // If this install has site config sources, load them now.
+    $site_sources = id(new PhutilSymbolLoader())
+      ->setAncestorClass('PhabricatorConfigSiteSource')
+      ->loadObjects();
+    $site_sources = msort($site_sources, 'getPriority');
+    foreach ($site_sources as $site_source) {
+      $stack->pushSource($site_source);
+    }
+
     try {
       $stack->pushSource(
         id(new PhabricatorConfigDatabaseSource('default'))