diff --git a/src/Symfony/Component/Process/Process.php b/src/Symfony/Component/Process/Process.php
index 504b4c3bc567..bd00e1761c57 100644
--- a/src/Symfony/Component/Process/Process.php
+++ b/src/Symfony/Component/Process/Process.php
@@ -277,7 +277,7 @@ public function start(callable $callback = null)
             }
 
             foreach ($env as $k => $v) {
-                $envBackup[$k] = getenv($v);
+                $envBackup[$k] = getenv($k);
                 putenv(false === $v || null === $v ? $k : "$k=$v");
             }
             $env = null;
diff --git a/src/Symfony/Component/Process/Tests/ProcessTest.php b/src/Symfony/Component/Process/Tests/ProcessTest.php
index c51a116e7319..379dae2df717 100644
--- a/src/Symfony/Component/Process/Tests/ProcessTest.php
+++ b/src/Symfony/Component/Process/Tests/ProcessTest.php
@@ -1403,6 +1403,20 @@ public function testSetBadEnv()
         $this->assertSame('', $process->getErrorOutput());
     }
 
+    public function testEnvBackupDoesNotDeleteExistingVars()
+    {
+        putenv('existing_var=foo');
+        $process = $this->getProcess('php -r "echo getenv(\'new_test_var\');"');
+        $process->setEnv(array('existing_var' => 'bar', 'new_test_var' => 'foo'));
+        $process->inheritEnvironmentVariables();
+
+        $process->run();
+
+        $this->assertSame('foo', $process->getOutput());
+        $this->assertSame('foo', getenv('existing_var'));
+        $this->assertFalse(getenv('new_test_var'));
+    }
+
     public function testInheritEnvEnabled()
     {
         $process = $this->getProcess(self::$phpBin.' -r '.escapeshellarg('echo serialize($_SERVER);'), null, array('BAR' => 'BAZ'));