diff --git a/UPGRADE-4.3.md b/UPGRADE-4.3.md
index 189c995bbef3d..1e9f0de938b1e 100644
--- a/UPGRADE-4.3.md
+++ b/UPGRADE-4.3.md
@@ -23,6 +23,7 @@ Config
 Form
 ----
 
+ * Support for using integers as form names is deprecated and will lead to a type error in 5.0, use strings instead.
  * Using the `date_format`, `date_widget`, and `time_widget` options of the `DateTimeType` when the `widget` option is
    set to `single_text` is deprecated.
 
diff --git a/UPGRADE-5.0.md b/UPGRADE-5.0.md
index 62aae8234a2ef..00376d7a5d4e7 100644
--- a/UPGRADE-5.0.md
+++ b/UPGRADE-5.0.md
@@ -78,6 +78,7 @@ Finder
 Form
 ----
 
+ * Using integers as form names is not supported anymore, use strings instead.
  * Using the `date_format`, `date_widget`, and `time_widget` options of the `DateTimeType` when the `widget` option is
    set to `single_text` is not supported anymore.
  * The `getExtendedType()` method was removed from the `FormTypeExtensionInterface`. It is replaced by the the static
diff --git a/src/Symfony/Component/Form/CHANGELOG.md b/src/Symfony/Component/Form/CHANGELOG.md
index b6d83d613b01e..1c4f5dddba67a 100644
--- a/src/Symfony/Component/Form/CHANGELOG.md
+++ b/src/Symfony/Component/Form/CHANGELOG.md
@@ -4,6 +4,7 @@ CHANGELOG
 4.3.0
 -----
 
+ * deprecated support for using integers as form names, use strings instead
  * deprecated using the `date_format`, `date_widget`, and `time_widget` options of the `DateTimeType` when the `widget`
    option is set to `single_text`
  * added `block_prefix` option to `BaseType`.
diff --git a/src/Symfony/Component/Form/FormConfigBuilder.php b/src/Symfony/Component/Form/FormConfigBuilder.php
index 344751b15976d..5297dfa5348de 100644
--- a/src/Symfony/Component/Form/FormConfigBuilder.php
+++ b/src/Symfony/Component/Form/FormConfigBuilder.php
@@ -179,6 +179,10 @@ public function __construct($name, ?string $dataClass, EventDispatcherInterface
     {
         self::validateName($name);
 
+        if (\is_int($name)) {
+            @trigger_error('Using integers as form names is deprecated in Symfony 4.3 and will lead to a type error in 5.0. Use strings instead.', E_USER_DEPRECATED);
+        }
+
         if (null !== $dataClass && !class_exists($dataClass) && !interface_exists($dataClass, false)) {
             throw new InvalidArgumentException(sprintf('Class "%s" not found. Is the "data_class" form option set correctly?', $dataClass));
         }
diff --git a/src/Symfony/Component/Form/Tests/FormConfigTest.php b/src/Symfony/Component/Form/Tests/FormConfigTest.php
index 18dac5528f97f..94267e365fb53 100644
--- a/src/Symfony/Component/Form/Tests/FormConfigTest.php
+++ b/src/Symfony/Component/Form/Tests/FormConfigTest.php
@@ -12,6 +12,7 @@
 namespace Symfony\Component\Form\Tests;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\EventDispatcher\EventDispatcher;
 use Symfony\Component\Form\FormConfigBuilder;
 
 /**
@@ -52,9 +53,6 @@ public function getHtml4Ids()
             // For root forms, leading underscores will be stripped from the
             // "id" attribute to produce valid HTML4.
             ['_'],
-            // Integers are allowed
-            [0],
-            [123],
             // NULL is allowed
             [null],
             // Other types are not
@@ -83,6 +81,26 @@ public function testNameAcceptsOnlyNamesValidAsIdsInHtml4($name, $expectedExcept
         $this->assertSame((string) $name, $formConfigBuilder->getName());
     }
 
+    /**
+     * @group legacy
+     * @expectedDeprecation Using integers as form names is deprecated in Symfony 4.3 and will lead to a type error in 5.0. Use strings instead.
+     * @dataProvider getHtml4IntegerIds
+     */
+    public function testNameContainingOnlyDigitsPassedAsInteger($name)
+    {
+        $formConfigBuilder = new FormConfigBuilder($name, null, new EventDispatcher());
+
+        $this->assertSame((string) $name, $formConfigBuilder->getName());
+    }
+
+    public function getHtml4IntegerIds()
+    {
+        return [
+            [0],
+            [123],
+        ];
+    }
+
     public function testGetRequestHandlerCreatesNativeRequestHandlerIfNotSet()
     {
         $config = $this->getConfigBuilder()->getFormConfig();