diff --git a/arcanist_util/__phutil_library_map__.php b/arcanist_util/__phutil_library_map__.php
index e3117382b499049beb55973f6190dac666b07e94..84ebc7b0a137a625b2c5eea9545b8f94db0a41f5 100644
--- a/arcanist_util/__phutil_library_map__.php
+++ b/arcanist_util/__phutil_library_map__.php
@@ -46,7 +46,7 @@ if (class_exists('ArcanistWorkflow')) {
       'BaseDirectoryScopedFormatLinter' => 'cpp_linter/BaseDirectoryScopedFormatLinter.php',
       'FacebookArcanistConfiguration' => 'config/FacebookOldArcanistConfiguration.php',
       'FacebookFbcodeLintEngine' => 'lint_engine/FacebookFbcodeLintEngine.php',
-      'FacebookFbcodeUnitTestEngine' => 'unit_engine/FacebookFbcodeUnitTestEngine.php',
+      'FacebookFbcodeUnitTestEngine' => 'unit_engine/FacebookOldFbcodeUnitTestEngine.php',
       'FacebookHowtoevenLintEngine' => 'lint_engine/FacebookHowtoevenLintEngine.php',
       'FacebookHowtoevenLinter' => 'cpp_linter/FacebookHowtoevenLinter.php',
       'FbcodeClangFormatLinter' => 'cpp_linter/FbcodeClangFormatLinter.php',
diff --git a/arcanist_util/config/RocksDBCommonHelper.php b/arcanist_util/config/RocksDBCommonHelper.php
index 28ee90a905f703132bea44c2ef1f39b529c2557a..cc876c4573127908ec385a83144f4554195a087a 100644
--- a/arcanist_util/config/RocksDBCommonHelper.php
+++ b/arcanist_util/config/RocksDBCommonHelper.php
@@ -62,7 +62,9 @@ function getSteps($applyDiff, $diffID, $username, $test) {
     assert(strlen($diffID) > 0);
     assert(is_numeric($diffID));
 
-    $arcrc_content = exec("cat ~/.arcrc | gzip -f | base64 -w0");
+    $arcrc_content = (PHP_OS == "Darwin" ?
+        exec("cat ~/.arcrc | gzip -f | base64") :
+            exec("cat ~/.arcrc | gzip -f | base64 -w0"));
     assert(strlen($arcrc_content) > 0);
 
     // Sandcastle machines don't have arc setup. We copy the user certificate
@@ -257,7 +259,9 @@ function getSandcastleConfig() {
   // execute. Why compress the job definitions? Otherwise we run over the max
   // string size.
   $cmd = "echo " . base64_encode(json_encode($arg))
-         . " | gzip -f | base64 -w0";
+         . (PHP_OS == "Darwin" ?
+             " | gzip -f | base64" :
+                 " | gzip -f | base64 -w0");
   assert(strlen($cmd) > 0);
 
   $arg_encoded = shell_exec($cmd);
diff --git a/arcanist_util/unit_engine/FacebookFbcodeUnitTestEngine.php b/arcanist_util/unit_engine/FacebookFbcodeUnitTestEngine.php
index 985bd68fc26433eeeb55c90e4c4b9008044cd297..62c275f6a942ba1cae64fa5b8654d1c6ae7fca20 100644
--- a/arcanist_util/unit_engine/FacebookFbcodeUnitTestEngine.php
+++ b/arcanist_util/unit_engine/FacebookFbcodeUnitTestEngine.php
@@ -4,7 +4,7 @@
 // LICENSE file in the root directory of this source tree. An additional grant
 // of patent rights can be found in the PATENTS file in the same directory.
 
-class FacebookFbcodeUnitTestEngine extends ArcanistBaseUnitTestEngine {
+class FacebookFbcodeUnitTestEngine extends ArcanistUnitTestEngine {
 
   public function run() {
       // For a call to `arc call-conduit differential.updateunitresults` to
diff --git a/arcanist_util/unit_engine/FacebookOldFbcodeUnitTestEngine.php b/arcanist_util/unit_engine/FacebookOldFbcodeUnitTestEngine.php
new file mode 100644
index 0000000000000000000000000000000000000000..985bd68fc26433eeeb55c90e4c4b9008044cd297
--- /dev/null
+++ b/arcanist_util/unit_engine/FacebookOldFbcodeUnitTestEngine.php
@@ -0,0 +1,17 @@
+<?php
+// Copyright 2004-present Facebook. All Rights Reserved.
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree. An additional grant
+// of patent rights can be found in the PATENTS file in the same directory.
+
+class FacebookFbcodeUnitTestEngine extends ArcanistBaseUnitTestEngine {
+
+  public function run() {
+      // For a call to `arc call-conduit differential.updateunitresults` to
+      // succeed we need at least one entry here.
+      $result = new ArcanistUnitTestResult();
+      $result->setName("dummy_placeholder_entry");
+      $result->setResult(ArcanistUnitTestResult::RESULT_PASS);
+      return array($result);
+  }
+}