diff --git a/src/Symfony/Component/DependencyInjection/Container.php b/src/Symfony/Component/DependencyInjection/Container.php
index f383744f2121b..3a144de90d1e0 100644
--- a/src/Symfony/Component/DependencyInjection/Container.php
+++ b/src/Symfony/Component/DependencyInjection/Container.php
@@ -169,6 +169,10 @@ public function set($id, $service)
             throw new InvalidArgumentException('You cannot set service "service_container".');
         }
 
+        if (isset($this->aliases[$id])) {
+            unset($this->aliases[$id]);
+        }
+
         $this->services[$id] = $service;
 
         if (null === $service) {
diff --git a/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php b/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php
index f252b56b13b64..927ab1b7ddfec 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php
@@ -231,6 +231,16 @@ public function testAddAliases()
         $this->assertTrue(isset($aliases['foobar']));
     }
 
+    public function testSetReplacesAlias()
+    {
+        $builder = new ContainerBuilder();
+        $builder->setAlias('alias', 'aliased');
+        $builder->set('aliased', new \stdClass());
+
+        $builder->set('alias', $foo = new \stdClass());
+        $this->assertSame($foo, $builder->get('alias'), '->set() replaces an existing alias');
+    }
+
     public function testAddGetCompilerPass()
     {
         $builder = new ContainerBuilder();
diff --git a/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php b/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
index 17b6ee6e9c79a..a9f41c56a22bb 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
@@ -142,6 +142,14 @@ public function testSetWithNullResetTheService()
         $this->assertFalse($sc->has('foo'), '->set() with null service resets the service');
     }
 
+    public function testSetReplacesAlias()
+    {
+        $c = new ProjectServiceContainer();
+
+        $c->set('alias', $foo = new \stdClass());
+        $this->assertSame($foo, $c->get('alias'), '->set() replaces an existing alias');
+    }
+
     public function testGet()
     {
         $sc = new ProjectServiceContainer();