diff --git a/src/applications/aphlict/management/PhabricatorAphlictManagementBuildWorkflow.php b/src/applications/aphlict/management/PhabricatorAphlictManagementBuildWorkflow.php
index b2665c47a1..bbee1c57f6 100644
--- a/src/applications/aphlict/management/PhabricatorAphlictManagementBuildWorkflow.php
+++ b/src/applications/aphlict/management/PhabricatorAphlictManagementBuildWorkflow.php
@@ -1,53 +1,61 @@
 <?php
 
 final class PhabricatorAphlictManagementBuildWorkflow
   extends PhabricatorAphlictManagementWorkflow {
 
   public function didConstruct() {
     $this
       ->setName('build')
       ->setSynopsis(pht('Build the Aphlict client.'))
       ->setArguments(
         array(
           array(
             'name' => 'debug',
             'help' => 'Enable a debug build.',
           ),
         ));
   }
 
   public function execute(PhutilArgumentParser $args) {
     $console = PhutilConsole::getConsole();
     $root = dirname(__FILE__).'/../../../..';
 
     if (!Filesystem::binaryExists('mxmlc')) {
-      $console->writeErr('`mxmlc` is not installed.');
-      return 1;
+      throw new PhutilArgumentUsageException(
+        pht(
+          "The `mxmlc` binary was not found in PATH. This compiler binary ".
+          "is required to rebuild the Aphlict client.\n\n".
+          "Adjust your PATH, or install the Flex SDK from:\n\n".
+          "    http://flex.apache.org\n\n".
+          "You may also be able to install it with `npm`:\n\n".
+          "    $ npm install flex-sdk\n\n".
+          "(Note: you should only need to rebuild Aphlict if you are ".
+          "developing Phabricator.)"));
     }
 
     $argv = array(
       "-source-path=$root/externals/vegas/src",
       '-static-link-runtime-shared-libraries=true',
       '-warnings=true',
       '-strict=true',
     );
 
     if ($args->getArg('debug')) {
       $argv[] = '-debug=true';
     }
 
     list ($err, $stdout, $stderr) = exec_manual('mxmlc %Ls -output=%s %s',
       $argv,
       $root.'/webroot/rsrc/swf/aphlict.swf',
       $root.'/support/aphlict/client/src/AphlictClient.as');
 
     if ($err) {
       $console->writeErr($stderr);
       return 1;
     }
 
     $console->writeOut("Done.\n");
     return 0;
   }
 
 }