diff --git a/src/Server/Environment.php b/src/Server/Environment.php
index 85f0695d..5429ebf3 100644
--- a/src/Server/Environment.php
+++ b/src/Server/Environment.php
@@ -25,7 +25,14 @@ class Environment
      * @var \Deployer\Type\DotArray
      */
     private $values = null;
-    
+
+    /**
+     * Values represented by their keys here are protected, and cannot be
+     * changed by calling the `set` method.
+     * @var array
+     */
+    private $protectedValueKeys = [];
+
     /**
      * Constructor
      */
@@ -37,10 +44,19 @@ class Environment
     /**
      * @param string $name
      * @param bool|int|string|array $value
+     * @param bool $isProtected
      */
-    public function set($name, $value)
+    public function set($name, $value, $isProtected = false)
     {
+        if (in_array($name, $this->protectedValueKeys)) {
+            throw new \RuntimeException("The environment parameter `$name` has already been set, and is protected from changes.");
+        }
+
         $this->values[$name] = $value;
+
+        if ($isProtected === true) {
+            $this->protectedValueKeys[] = $name;
+        }
     }
 
     /**
diff --git a/test/src/Server/EnvironmentTest.php b/test/src/Server/EnvironmentTest.php
index 333df66a..d35b2105 100644
--- a/test/src/Server/EnvironmentTest.php
+++ b/test/src/Server/EnvironmentTest.php
@@ -4,7 +4,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
- 
+
 namespace Deployer\Server;
 
 class EnvironmentTest extends \PHPUnit_Framework_TestCase
@@ -30,7 +30,7 @@ class EnvironmentTest extends \PHPUnit_Framework_TestCase
         $env->set('string', 'value');
         $env->set('array', [1, 'two']);
         $env->set('parse', 'is {{int}}');
-        
+
         $this->assertEquals(42, $env->get('int'));
         $this->assertEquals('value', $env->get('string'));
         $this->assertEquals([1, 'two'], $env->get('array'));
@@ -45,4 +45,14 @@ class EnvironmentTest extends \PHPUnit_Framework_TestCase
         $this->setExpectedException('RuntimeException', 'Environment parameter `so` does not exists.');
         $env->get('so');
     }
+
+    public function testProtectedParameters()
+    {
+        $env = new Environment();
+
+        $env->set('protected', 'protected-value', true);
+
+        $this->setExpectedException('\RuntimeException', 'The environment parameter `protected` has already been set, and is protected from changes.');
+        $env->set('protected', 'some-other-value');
+    }
 }