diff --git a/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php b/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php
index 843522a0fc..da4d53d09a 100644
--- a/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php
+++ b/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php
@@ -13,6 +13,10 @@ namespace Symfony\Bridge\PhpUnit;
 
 use Doctrine\Common\Annotations\AnnotationRegistry;
 
+if (!class_exists('PHPUnit_Framework_BaseTestListener')) {
+    return;
+}
+
 /**
  * Collects and replays skipped tests.
  *
diff --git a/src/Symfony/Bridge/PhpUnit/TextUI/Command.php b/src/Symfony/Bridge/PhpUnit/TextUI/Command.php
index 203fd16414..d4ffeac3fd 100644
--- a/src/Symfony/Bridge/PhpUnit/TextUI/Command.php
+++ b/src/Symfony/Bridge/PhpUnit/TextUI/Command.php
@@ -11,6 +11,10 @@
 
 namespace Symfony\Bridge\PhpUnit\TextUI;
 
+if (!class_exists('PHPUnit_TextUI_Command')) {
+    return;
+}
+
 /**
  * {@inheritdoc}
  */
diff --git a/src/Symfony/Bridge/PhpUnit/TextUI/TestRunner.php b/src/Symfony/Bridge/PhpUnit/TextUI/TestRunner.php
index 94602bb3d6..16c5f078e6 100644
--- a/src/Symfony/Bridge/PhpUnit/TextUI/TestRunner.php
+++ b/src/Symfony/Bridge/PhpUnit/TextUI/TestRunner.php
@@ -13,6 +13,10 @@ namespace Symfony\Bridge\PhpUnit\TextUI;
 
 use Symfony\Bridge\PhpUnit\SymfonyTestsListener;
 
+if (!class_exists('PHPUnit_TextUI_TestRunner')) {
+    return;
+}
+
 /**
  * {@inheritdoc}
  */
diff --git a/src/Symfony/Bundle/SecurityBundle/composer.json b/src/Symfony/Bundle/SecurityBundle/composer.json
index 12a16ed7af..2568236ce5 100644
--- a/src/Symfony/Bundle/SecurityBundle/composer.json
+++ b/src/Symfony/Bundle/SecurityBundle/composer.json
@@ -27,7 +27,7 @@
         "symfony/console": "~2.8|~3.0",
         "symfony/css-selector": "~2.8|~3.0",
         "symfony/dom-crawler": "~2.8|~3.0",
-        "symfony/form": "~2.8|~3.0",
+        "symfony/form": "^2.8.18|^3.2.5",
         "symfony/framework-bundle": "^3.2.5",
         "symfony/http-foundation": "~2.8|~3.0",
         "symfony/security-acl": "~2.8|~3.0",
@@ -35,7 +35,7 @@
         "symfony/twig-bundle": "~2.8|~3.0",
         "symfony/twig-bridge": "~2.8|~3.0",
         "symfony/process": "~2.8|~3.0",
-        "symfony/validator": "~2.8|~3.0",
+        "symfony/validator": "^2.8.18|^3.2.5",
         "symfony/var-dumper": "~3.2",
         "symfony/yaml": "~2.8|~3.0",
         "symfony/expression-language": "~2.8|~3.0",