diff --git a/src/Symfony/Component/Process/Process.php b/src/Symfony/Component/Process/Process.php
index 830c623e0dc3..dc386aa52693 100644
--- a/src/Symfony/Component/Process/Process.php
+++ b/src/Symfony/Component/Process/Process.php
@@ -272,7 +272,7 @@ public function start(callable $callback = null/*, array $env = array()*/)
         } else {
             if (__CLASS__ !== static::class) {
                 $r = new \ReflectionMethod($this, __FUNCTION__);
-                if (__CLASS__ !== $r->getDeclaringClass()->getName() && (2 > $r->getNumberOfParameters() || 'env' !== $r->getParameters()[0]->name)) {
+                if (__CLASS__ !== $r->getDeclaringClass()->getName() && (2 > $r->getNumberOfParameters() || 'env' !== $r->getParameters()[1]->name)) {
                     @trigger_error(sprintf('The %s::start() method expects a second "$env" argument since Symfony 3.3. It will be made mandatory in 4.0.', static::class), E_USER_DEPRECATED);
                 }
             }