diff --git a/src/unit/engine/PytestTestEngine.php b/src/unit/engine/PytestTestEngine.php
index f9014dad..b104d8fc 100644
--- a/src/unit/engine/PytestTestEngine.php
+++ b/src/unit/engine/PytestTestEngine.php
@@ -25,7 +25,7 @@ final class PytestTestEngine extends ArcanistUnitTestEngine {
   public function buildTestFuture($junit_tmp, $cover_tmp) {
     $paths = $this->getPaths();
 
-    $cmd_line = csprintf('py.test --junitxml %s', $junit_tmp);
+    $cmd_line = csprintf('py.test --junit-xml=%s', $junit_tmp);
 
     if ($this->getEnableCoverage() !== false) {
       $cmd_line = csprintf(