diff --git a/src/filesystem/__tests__/PhutilDeferredLogTestCase.php b/src/filesystem/__tests__/PhutilDeferredLogTestCase.php
--- a/src/filesystem/__tests__/PhutilDeferredLogTestCase.php
+++ b/src/filesystem/__tests__/PhutilDeferredLogTestCase.php
@@ -94,28 +94,6 @@
     $this->assertTrue($caught instanceof Exception);
   }
 
-  public function testManyWriters() {
-    $root = phutil_get_library_root('arcanist').'/../';
-    $bin = $root.'scripts/test/deferred_log.php';
-
-    $n_writers = 3;
-    $n_lines   = 8;
-
-    $tmp = new TempFile();
-
-    $futures = array();
-    for ($ii = 0; $ii < $n_writers; $ii++) {
-      $futures[] = new ExecFuture('%s %d %s', $bin, $n_lines, (string)$tmp);
-    }
-
-    id(new FutureIterator($futures))
-      ->resolveAll();
-
-    $this->assertEqual(
-      str_repeat("abcdefghijklmnopqrstuvwxyz\n", $n_writers * $n_lines),
-      Filesystem::readFile($tmp));
-  }
-
   public function testNoWrite() {
     $tmp = new TempFile();
 
diff --git a/src/filesystem/__tests__/PhutilFileLockTestCase.php b/src/filesystem/__tests__/PhutilFileLockTestCase.php
--- a/src/filesystem/__tests__/PhutilFileLockTestCase.php
+++ b/src/filesystem/__tests__/PhutilFileLockTestCase.php
@@ -172,11 +172,13 @@
 
   private function buildLockFuture($flags, $file) {
     $root = dirname(phutil_get_library_root('arcanist'));
-    $bin = $root.'/scripts/utils/lock.php';
+    $bin = $root.'/support/test/lock-file.php';
+
+    $flags = (array)$flags;
 
     // NOTE: Use `exec` so this passes on Ubuntu, where the default `dash` shell
     // will eat any kills we send during the tests.
-    $future = new ExecFuture('exec php %s %C %s', $bin, $flags, $file);
+    $future = new ExecFuture('exec php -f %R -- %Ls %R', $bin, $flags, $file);
     $future->start();
     return $future;
   }
diff --git a/support/test/lock-file.php b/support/test/lock-file.php
new file mode 100644
--- /dev/null
+++ b/support/test/lock-file.php
@@ -0,0 +1,82 @@
+#!/usr/bin/env php
+<?php
+
+require_once dirname(__FILE__).'/../../scripts/init/init-script.php';
+
+$args = new PhutilArgumentParser($argv);
+$args->setTagline(pht('acquire and hold a lockfile'));
+$args->setSynopsis(<<<EOHELP
+**lock.php** __file__ [__options__]
+    Acquire a lockfile and hold it until told to unlock it.
+
+EOHELP
+);
+
+$args->parseStandardArguments();
+$args->parse(array(
+  array(
+    'name'      => 'test',
+    'help'      => pht('Instead of holding the lock, release it and exit.'),
+  ),
+  array(
+    'name'      => 'hold',
+    'help'      => pht('Hold indefinitely without prompting.'),
+  ),
+  array(
+    'name'      => 'wait',
+    'param'     => 'n',
+    'help'      => pht('Block for up to __n__ seconds waiting for the lock.'),
+    'default'   => 0,
+  ),
+  array(
+    'name'      => 'file',
+    'wildcard'  => true,
+  ),
+));
+
+
+$file = $args->getArg('file');
+if (count($file) !== 1) {
+  $args->printHelpAndExit();
+}
+$file = head($file);
+
+$console = PhutilConsole::getConsole();
+$console->writeOut(
+  "%s\n",
+  pht('This process has PID %d. Acquiring lock...', getmypid()));
+
+$lock = PhutilFileLock::newForPath($file);
+
+try {
+  $lock->lock($args->getArg('wait'));
+} catch (PhutilFileLockException $ex) {
+  $console->writeOut(
+    "**%s** %s\n",
+    pht('UNABLE TO ACQUIRE LOCK:'),
+    pht('Lock is already held.'));
+  exit(1);
+}
+
+// NOTE: This string is magic, the unit tests look for it.
+$console->writeOut("%s\n", pht('LOCK ACQUIRED'));
+if ($args->getArg('test')) {
+  $lock->unlock();
+  exit(0);
+}
+
+if ($args->getArg('hold')) {
+  while (true) {
+    sleep(1);
+  }
+}
+
+while (!$console->confirm(pht('Release lock?'))) {
+  // Keep asking until they say yes.
+}
+
+$console->writeOut("%s\n", pht('Unlocking...'));
+$lock->unlock();
+
+$console->writeOut("%s\n", pht('Done.'));
+exit(0);