diff --git a/scripts/daemon/phabricator_daemon_launcher.php b/scripts/daemon/phabricator_daemon_launcher.php
index b2e0534d67..a67a8ace57 100755
--- a/scripts/daemon/phabricator_daemon_launcher.php
+++ b/scripts/daemon/phabricator_daemon_launcher.php
@@ -1,176 +1,186 @@
 #!/usr/bin/env php
 <?php
 
 $root = dirname(dirname(dirname(__FILE__)));
 require_once $root.'/scripts/__init_script__.php';
 
 $control = new PhabricatorDaemonControl();
 
 must_have_extension('pcntl');
 must_have_extension('posix');
 
 function must_have_extension($ext) {
   if (!extension_loaded($ext)) {
     echo "ERROR: The PHP extension '{$ext}' is not installed. You must ".
          "install it to run daemons on this machine.\n";
     exit(1);
   }
+
+  $extension = new ReflectionExtension($ext);
+  foreach ($extension->getFunctions() as $function) {
+    $function = $function->name;
+    if (!function_exists($function)) {
+      echo "ERROR: The PHP function {$function}() is disabled. You must ".
+           "enable it to run daemons on this machine.\n";
+      exit(1);
+    }
+  }
 }
 
 $command = isset($argv[1]) ? $argv[1] : 'help';
 switch ($command) {
   case 'list':
     $err = $control->executeListCommand();
     exit($err);
 
   case 'status':
     $err = $control->executeStatusCommand();
     exit($err);
 
   case 'stop':
     $pass_argv = array_slice($argv, 2);
     $err = $control->executeStopCommand($pass_argv);
     exit($err);
 
   case 'restart':
     $err = $control->executeStopCommand(array());
     if ($err) {
       exit($err);
     }
     /* Fall Through */
   case 'start':
     $running = $control->loadRunningDaemons();
     // "running" might not mean actually running so much as was running at
     // some point. ergo, do a quick grouping and only barf if daemons are
     // *actually* running.
     $running_dict = mgroup($running, 'isRunning');
     if (!empty($running_dict[true])) {
       echo phutil_console_wrap(
         "phd start: Unable to start daemons because daemons are already ".
         "running.\n".
         "You can view running daemons with 'phd status'.\n".
         "You can stop running daemons with 'phd stop'.\n".
         "You can use 'phd restart' to stop all daemons before starting new ".
         "daemons.\n");
       exit(1);
     }
 
     $daemons = array(
       array('PhabricatorRepositoryPullLocalDaemon', array()),
       array('PhabricatorGarbageCollectorDaemon', array()),
     );
 
     $taskmasters = PhabricatorEnv::getEnvConfig('phd.start-taskmasters');
     for ($ii = 0; $ii < $taskmasters; $ii++) {
       $daemons[] = array('PhabricatorTaskmasterDaemon', array());
     }
 
     will_launch($control);
     foreach ($daemons as $spec) {
       list($name, $argv) = $spec;
       echo "Launching '{$name}'...\n";
       $control->launchDaemon($name, $argv);
     }
 
     echo "Done.\n";
     break;
 
   case 'launch':
   case 'debug':
     $is_debug = ($argv[1] == 'debug');
 
     $daemon = idx($argv, 2);
     if (!$daemon) {
       throw new Exception("Daemon name required!");
     }
 
     $pass_argv = array_slice($argv, 3);
 
     $n = 1;
     if (!$is_debug) {
       if (is_numeric($daemon)) {
         $n = $daemon;
         if ($n < 1) {
           throw new Exception("Count must be at least 1!");
         }
         $daemon = idx($argv, 3);
         if (!$daemon) {
           throw new Exception("Daemon name required!");
         }
         $pass_argv = array_slice($argv, 4);
       }
     }
 
     $loader = new PhutilSymbolLoader();
     $symbols = $loader
       ->setAncestorClass('PhutilDaemon')
       ->selectSymbolsWithoutLoading();
 
     $symbols = ipull($symbols, 'name');
     $match = array();
     foreach ($symbols as $symbol) {
       if (stripos($symbol, $daemon) !== false) {
         if (strtolower($symbol) == strtolower($daemon)) {
           $match = array($symbol);
           break;
         } else {
           $match[] = $symbol;
         }
       }
     }
 
     if (count($match) == 0) {
       throw new Exception(
         "No daemons match! Use 'phd list' for a list of daemons.");
     } else if (count($match) > 1) {
       throw new Exception(
         "Which of these daemons did you mean?\n".
         "    ".implode("\n    ", $match));
     } else {
       $daemon = reset($match);
     }
 
     $with_logs = true;
     if ($is_debug) {
       // In debug mode, we emit errors straight to stdout, so nothing useful
       // will show up in the logs. Don't echo the message about stuff showing
       // up in them, since it would be confusing.
       $with_logs = false;
     }
 
     will_launch($control, $with_logs);
 
     if ($is_debug) {
       echo "Launching {$daemon} in debug mode (nondaemonized)...\n";
     } else {
       echo "Launching {$n} x {$daemon}";
     }
 
     for ($ii = 0; $ii < $n; $ii++) {
       $control->launchDaemon($daemon, $pass_argv, $is_debug);
       if (!$is_debug) {
         echo ".";
       }
     }
 
     echo "\n";
     echo "Done.\n";
 
     break;
 
   case '--help':
   case 'help':
   default:
     $err = $control->executeHelpCommand();
     exit($err);
 }
 
 function will_launch($control, $with_logs = true) {
   echo "Staging launch...\n";
   $control->pingConduit();
   if ($with_logs) {
     $log_dir = $control->getLogDirectory().'/daemons.log';
     echo "NOTE: Logs will appear in '{$log_dir}'.\n\n";
   }
 }