diff --git a/scripts/__init_script__.php b/scripts/__init_script__.php
--- a/scripts/__init_script__.php
+++ b/scripts/__init_script__.php
@@ -1,11 +1,5 @@
 <?php
 
-if (function_exists('pcntl_async_signals')) {
-  pcntl_async_signals(true);
-} else {
-  declare(ticks = 1);
-}
-
 function __phutil_init_script__() {
   // Adjust the runtime language configuration to be reasonable and inline with
   // expectations. We do this first, then load libraries.
@@ -86,6 +80,11 @@
   require_once $root.'/src/__phutil_library_init__.php';
 
   PhutilErrorHandler::initialize();
+
+  // If "variables_order" excludes "E", silently repair it so that $_ENV has
+  // the values we expect.
+  PhutilExecutionEnvironment::repairMissingVariablesOrder();
+
   $router = PhutilSignalRouter::initialize();
 
   $handler = new PhutilBacktraceSignalHandler();
diff --git a/src/utils/PhutilExecutionEnvironment.php b/src/utils/PhutilExecutionEnvironment.php
--- a/src/utils/PhutilExecutionEnvironment.php
+++ b/src/utils/PhutilExecutionEnvironment.php
@@ -13,4 +13,34 @@
     return php_uname('r');
   }
 
+  /**
+   * If the PHP configuration setting "variables_order" does not include "E",
+   * the `$_ENV` superglobal is not populated with the containing environment.
+   * For details, see T12071.
+   *
+   * This can be fixed by adding "E" to the configuration, but we can also
+   * repair it ourselves by re-executing a subprocess with the configuration
+   * option defined to include "E". This is clumsy, but saves users from
+   * needing to go find and edit their PHP files.
+   *
+   * @return void
+   */
+  public static function repairMissingVariablesOrder() {
+    $variables_order = ini_get('variables_order');
+    $variables_order = strtoupper($variables_order);
+
+    if (strpos($variables_order, 'E') !== false) {
+      // The "variables_order" option already has "E", so we don't need to
+      // repair $_ENV.
+      return;
+    }
+
+    list($env) = execx(
+      'php -d variables_order=E -r %s',
+      'echo json_encode($_ENV);');
+    $env = phutil_json_decode($env);
+
+    $_ENV = $_ENV + $env;
+  }
+
 }