diff --git a/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php b/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
index e4314648df8d..7ed2f3217183 100644
--- a/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
+++ b/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
@@ -53,7 +53,7 @@ public function getTypeExtensions($name)
         $extensions = [];
 
         if (isset($this->typeExtensionServices[$name])) {
-            foreach ($this->typeExtensionServices[$name] as $serviceId => $extension) {
+            foreach ($this->typeExtensionServices[$name] as $extension) {
                 $extensions[] = $extension;
 
                 if (method_exists($extension, 'getExtendedTypes')) {
@@ -68,7 +68,7 @@ public function getTypeExtensions($name)
 
                 // validate the result of getExtendedTypes()/getExtendedType() to ensure it is consistent with the service definition
                 if (!\in_array($name, $extendedTypes, true)) {
-                    throw new InvalidArgumentException(sprintf('The extended type specified for the service "%s" does not match the actual extended type. Expected "%s", given "%s".', $serviceId, $name, implode(', ', $extendedTypes)));
+                    throw new InvalidArgumentException(sprintf('The extended type "%s" specified for the type extension class "%s" does not match any of the actual extended types (["%s"]).', $name, \get_class($extension), implode('", "', $extendedTypes)));
                 }
             }
         }
diff --git a/src/Symfony/Component/Form/Tests/Extension/DependencyInjection/DependencyInjectionExtensionTest.php b/src/Symfony/Component/Form/Tests/Extension/DependencyInjection/DependencyInjectionExtensionTest.php
index 923ad8a38f61..26db2d8cea28 100644
--- a/src/Symfony/Component/Form/Tests/Extension/DependencyInjection/DependencyInjectionExtensionTest.php
+++ b/src/Symfony/Component/Form/Tests/Extension/DependencyInjection/DependencyInjectionExtensionTest.php
@@ -44,6 +44,8 @@ public function testGetTypeExtensions()
     public function testThrowExceptionForInvalidExtendedType()
     {
         $this->expectException('Symfony\Component\Form\Exception\InvalidArgumentException');
+        $this->expectExceptionMessage(sprintf('The extended type "unmatched" specified for the type extension class "%s" does not match any of the actual extended types (["test"]).', TestTypeExtension::class));
+
         $extensions = [
             'unmatched' => new \ArrayIterator([new TestTypeExtension()]),
         ];