diff --git a/src/unit/engine/ArcanistUnitTestEngine.php b/src/unit/engine/ArcanistUnitTestEngine.php
--- a/src/unit/engine/ArcanistUnitTestEngine.php
+++ b/src/unit/engine/ArcanistUnitTestEngine.php
@@ -8,7 +8,6 @@
   private $workingCopy;
   private $paths = array();
   private $arguments = array();
-  private $enableAsyncTests;
   private $enableCoverage;
   private $runAllTests;
   private $configurationManager;
@@ -80,15 +79,6 @@
     return idx($this->arguments, $key, $default);
   }
 
-  final public function setEnableAsyncTests($enable_async_tests) {
-    $this->enableAsyncTests = $enable_async_tests;
-    return $this;
-  }
-
-  final public function getEnableAsyncTests() {
-    return $this->enableAsyncTests;
-  }
-
   final public function setEnableCoverage($enable_coverage) {
     $this->enableCoverage = $enable_coverage;
     return $this;
diff --git a/src/workflow/ArcanistUnitWorkflow.php b/src/workflow/ArcanistUnitWorkflow.php
--- a/src/workflow/ArcanistUnitWorkflow.php
+++ b/src/workflow/ArcanistUnitWorkflow.php
@@ -165,13 +165,6 @@
     }
     $this->engine->setEnableCoverage($enable_coverage);
 
-    // Enable possible async tests only for 'arc diff' not 'arc unit'
-    if ($this->getParentWorkflow()) {
-      $this->engine->setEnableAsyncTests(true);
-    } else {
-      $this->engine->setEnableAsyncTests(false);
-    }
-
     $results = $this->engine->run();
 
     $this->validateUnitEngineResults($this->engine, $results);