diff --git a/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php b/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
index 6a0d9aec99..43394cea79 100644
--- a/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
+++ b/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
@@ -262,6 +262,7 @@ class SymfonyTestsListenerTrait
         if ($this->runsInSeparateProcess) {
             $deprecations = file_get_contents($this->runsInSeparateProcess);
             unlink($this->runsInSeparateProcess);
+            putenv('SYMFONY_DEPRECATIONS_SERIALIZE');
             foreach ($deprecations ? unserialize($deprecations) : array() as $deprecation) {
                 if ($deprecation[0]) {
                     trigger_error(serialize(array('deprecation' => $deprecation[1], 'class' => $className, 'method' => $test->getName(false))), E_USER_DEPRECATED);
diff --git a/src/Symfony/Bridge/PhpUnit/bootstrap.php b/src/Symfony/Bridge/PhpUnit/bootstrap.php
index 2803caf02b..a265a129e6 100644
--- a/src/Symfony/Bridge/PhpUnit/bootstrap.php
+++ b/src/Symfony/Bridge/PhpUnit/bootstrap.php
@@ -12,12 +12,15 @@
 use Doctrine\Common\Annotations\AnnotationRegistry;
 use Symfony\Bridge\PhpUnit\DeprecationErrorHandler;
 
+// Detect if we need to serialize deprecations to a file.
+if ($file = getenv('SYMFONY_DEPRECATIONS_SERIALIZE')) {
+    DeprecationErrorHandler::collectDeprecations($file);
+
+    return;
+}
+
 // Detect if we're loaded by an actual run of phpunit
 if (!defined('PHPUNIT_COMPOSER_INSTALL') && !class_exists('PHPUnit_TextUI_Command', false) && !class_exists('PHPUnit\TextUI\Command', false)) {
-    if ($ser = getenv('SYMFONY_DEPRECATIONS_SERIALIZE')) {
-        DeprecationErrorHandler::collectDeprecations($ser);
-    }
-
     return;
 }