diff --git a/src/Symfony/Component/DependencyInjection/Container.php b/src/Symfony/Component/DependencyInjection/Container.php
index 81241e3415cc..6eceb0defeba 100644
--- a/src/Symfony/Component/DependencyInjection/Container.php
+++ b/src/Symfony/Component/DependencyInjection/Container.php
@@ -438,13 +438,13 @@ protected function getEnv($name)
         if (isset($this->envCache[$name]) || array_key_exists($name, $this->envCache)) {
             return $this->envCache[$name];
         }
-        if (0 !== strpos($name, 'HTTP_') && isset($_SERVER[$name])) {
+        if (isset($_SERVER[$name]) && 0 !== strpos($name, 'HTTP_')) {
             return $this->envCache[$name] = $_SERVER[$name];
         }
         if (isset($_ENV[$name])) {
             return $this->envCache[$name] = $_ENV[$name];
         }
-        if (false !== $env = getenv($name)) {
+        if (false !== ($env = getenv($name)) && null !== $env) { // null is a possible value because of thread safety issues
             return $this->envCache[$name] = $env;
         }
         if (!$this->hasParameter("env($name)")) {
diff --git a/src/Symfony/Component/Dotenv/Dotenv.php b/src/Symfony/Component/Dotenv/Dotenv.php
index 0d3c01d93639..910a1622f303 100644
--- a/src/Symfony/Component/Dotenv/Dotenv.php
+++ b/src/Symfony/Component/Dotenv/Dotenv.php
@@ -70,13 +70,17 @@ public function populate($values)
         unset($loadedVars['']);
 
         foreach ($values as $name => $value) {
-            if (!isset($loadedVars[$name]) && (isset($_ENV[$name]) || isset($_SERVER[$name]) || false !== getenv($name))) {
+            $notHttpName = 0 !== strpos($name, 'HTTP_');
+            // don't check existence with getenv() because of thread safety issues
+            if (!isset($loadedVars[$name]) && (isset($_ENV[$name]) || (isset($_SERVER[$name]) && $notHttpName))) {
                 continue;
             }
 
             putenv("$name=$value");
             $_ENV[$name] = $value;
-            $_SERVER[$name] = $value;
+            if ($notHttpName) {
+                $_SERVER[$name] = $value;
+            }
 
             $loadedVars[$name] = true;
         }
@@ -363,7 +367,15 @@ private function resolveVariables($value)
             }
 
             $name = $matches[3];
-            $value = isset($this->values[$name]) ? $this->values[$name] : (isset($_ENV[$name]) ? $_ENV[$name] : (string) getenv($name));
+            if (isset($this->values[$name])) {
+                $value = $this->values[$name];
+            } elseif (isset($_SERVER[$name]) && 0 !== strpos($name, 'HTTP_')) {
+                $value = $_SERVER[$name];
+            } elseif (isset($_ENV[$name])) {
+                $value = $_ENV[$name];
+            } else {
+                $value = (string) getenv($name);
+            }
 
             if (!$matches[2] && isset($matches[4])) {
                 $value .= '}';
diff --git a/src/Symfony/Component/Dotenv/Tests/DotenvTest.php b/src/Symfony/Component/Dotenv/Tests/DotenvTest.php
index dc1a7b5b2c4a..ce7d3a93396b 100644
--- a/src/Symfony/Component/Dotenv/Tests/DotenvTest.php
+++ b/src/Symfony/Component/Dotenv/Tests/DotenvTest.php
@@ -208,6 +208,7 @@ public function testServerSuperglobalIsNotOverriden()
     public function testEnvVarIsNotOverriden()
     {
         putenv('TEST_ENV_VAR=original_value');
+        $_SERVER['TEST_ENV_VAR'] = 'original_value';
 
         $dotenv = new DotEnv();
         $dotenv->populate(array('TEST_ENV_VAR' => 'new_value'));
@@ -215,6 +216,18 @@ public function testEnvVarIsNotOverriden()
         $this->assertSame('original_value', getenv('TEST_ENV_VAR'));
     }
 
+    public function testHttpVarIsPartiallyOverriden()
+    {
+        $_SERVER['HTTP_TEST_ENV_VAR'] = 'http_value';
+
+        $dotenv = new DotEnv();
+        $dotenv->populate(array('HTTP_TEST_ENV_VAR' => 'env_value'));
+
+        $this->assertSame('env_value', getenv('HTTP_TEST_ENV_VAR'));
+        $this->assertSame('env_value', $_ENV['HTTP_TEST_ENV_VAR']);
+        $this->assertSame('http_value', $_SERVER['HTTP_TEST_ENV_VAR']);
+    }
+
     public function testMemorizingLoadedVarsNamesInSpecialVar()
     {
         // Special variable not exists