diff --git a/src/future/exec/PhutilExecutableFuture.php b/src/future/exec/PhutilExecutableFuture.php
index c4a5432..a053c3d 100644
--- a/src/future/exec/PhutilExecutableFuture.php
+++ b/src/future/exec/PhutilExecutableFuture.php
@@ -1,133 +1,155 @@
 <?php
 
 /**
  * @task config Configuring the Command
  */
 abstract class PhutilExecutableFuture extends Future {
 
 
   private $env;
   private $cwd;
 
 
   /**
    * Set environmental variables for the command.
    *
    * By default, variables are added to the environment of this process. You
    * can optionally wipe the environment and pass only the specified values.
    *
    *   // Env will have "X" and current env ("PATH", etc.)
    *   $exec->setEnv(array('X' => 'y'));
    *
    *   // Env will have ONLY "X".
    *   $exec->setEnv(array('X' => 'y'), $wipe_process_env = true);
    *
    * @param map<string, string> Dictionary of environmental variables.
    * @param bool Optionally, pass `true` to replace the existing environment.
    * @return this
    *
    * @task config
    */
   final public function setEnv(array $env, $wipe_process_env = false) {
     // Force values to strings here. The underlying PHP commands get upset if
     // they are handed non-string values as environmental variables.
     foreach ($env as $key => $value) {
       $env[$key] = (string)$value;
     }
 
     if (!$wipe_process_env) {
       $env = $env + $this->getEnv();
     }
 
     $this->env = $env;
 
     return $this;
   }
 
 
   /**
    * Set the value of a specific environmental variable for this command.
    *
    * @param string Environmental variable name.
    * @param string|null New value, or null to remove this variable.
    * @return this
    * @task config
    */
   final public function updateEnv($key, $value) {
     $env = $this->getEnv();
 
     if ($value === null) {
       unset($env[$key]);
     } else {
       $env[$key] = (string)$value;
     }
 
     $this->env = $env;
 
     return $this;
   }
 
 
   /**
    * Returns `true` if this command has a configured environment.
    *
    * @return bool True if this command has an environment.
    * @task config
    */
   final public function hasEnv() {
     return ($this->env !== null);
   }
 
 
   /**
    * Get the configured environment.
    *
    * @return map<string, string> Effective environment for this command.
    * @task config
    */
   final public function getEnv() {
     if (!$this->hasEnv()) {
-      $this->setEnv($_ENV, $wipe_process_env = true);
+      $default_env = $_ENV;
+
+      // If `variables_order` does not include "E", the $_ENV superglobal
+      // does not build and there's no apparent reasonable way for us to
+      // rebuild it (we could perhaps parse the output of `export`).
+
+      // For now, explicitly populate variables which we rely on and which
+      // we know may exist. After T12071, we should be able to rely on
+      // $_ENV and no longer need to do this.
+
+      $known_keys = array(
+        'PHABRICATOR_ENV',
+        'PHABRICATOR_INSTANCE',
+      );
+
+      foreach ($known_keys as $known_key) {
+        $value = getenv($known_key);
+        if (strlen($value)) {
+          $default_env[$known_key] = $value;
+        }
+      }
+
+      $this->setEnv($default_env, $wipe_process_env = true);
     }
 
     return $this->env;
   }
 
 
   /**
    * Set the current working directory for the subprocess (that is, set where
    * the subprocess will execute). If not set, the default value is the parent's
    * current working directory.
    *
    * @param string Directory to execute the subprocess in.
    * @return this
    * @task config
    */
   final public function setCWD($cwd) {
     $cwd = (string)$cwd;
 
     if (!is_dir($cwd)) {
       throw new Exception(
         pht(
           'Preparing to run a command in directory "%s", but that '.
           'directory does not exist.',
           $cwd));
     }
 
     $this->cwd = $cwd;
 
     return $this;
   }
 
 
   /**
    * Get the command's current working directory.
    *
    * @return string Working directory.
    * @task config
    */
   final public function getCWD() {
     return $this->cwd;
   }
 
 }