diff --git a/composer.json b/composer.json
index 2802a450d..f33756238 100644
--- a/composer.json
+++ b/composer.json
@@ -36,7 +36,8 @@
     },
     "autoload": {
         "files": [
-            "src/Resources/debug.php"
+            "src/Resources/debug.php",
+            "src/Resources/string_loader.php"
         ],
         "psr-4" : {
             "Twig\\" : "src/"
diff --git a/src/Extension/StringLoaderExtension.php b/src/Extension/StringLoaderExtension.php
index 7b4514710..fde395dd8 100644
--- a/src/Extension/StringLoaderExtension.php
+++ b/src/Extension/StringLoaderExtension.php
@@ -9,7 +9,10 @@
  * file that was distributed with this source code.
  */
 
-namespace Twig\Extension {
+namespace Twig\Extension;
+
+use Twig\Environment;
+use Twig\TemplateWrapper;
 use Twig\TwigFunction;
 
 final class StringLoaderExtension extends AbstractExtension
@@ -17,26 +20,22 @@ final class StringLoaderExtension extends AbstractExtension
     public function getFunctions(): array
     {
         return [
-            new TwigFunction('template_from_string', 'twig_template_from_string', ['needs_environment' => true]),
+            new TwigFunction('template_from_string', [self::class, 'templateFromString'], ['needs_environment' => true]),
         ];
     }
-}
-}
 
-namespace {
-use Twig\Environment;
-use Twig\TemplateWrapper;
-
-/**
- * Loads a template from a string.
- *
- *     {{ include(template_from_string("Hello {{ name }}")) }}
- *
- * @param string $template A template as a string or object implementing __toString()
- * @param string $name     An optional name of the template to be used in error messages
- */
-function twig_template_from_string(Environment $env, $template, string $name = null): TemplateWrapper
-{
-    return $env->createTemplate((string) $template, $name);
-}
+    /**
+     * Loads a template from a string.
+     *
+     *     {{ include(template_from_string("Hello {{ name }}")) }}
+     *
+     * @param string $template A template as a string or object implementing __toString()
+     * @param string $name     An optional name of the template to be used in error messages
+     * 
+     * @internal
+     */
+    public static function templateFromString(Environment $env, $template, string $name = null): TemplateWrapper
+    {
+        return $env->createTemplate((string) $template, $name);
+    }
 }
diff --git a/src/Resources/string_loader.php b/src/Resources/string_loader.php
new file mode 100644
index 000000000..b074495ca
--- /dev/null
+++ b/src/Resources/string_loader.php
@@ -0,0 +1,25 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+use Twig\Environment;
+use Twig\Extension\StringLoaderExtension;
+use Twig\TemplateWrapper;
+
+/**
+ * @internal
+ * @deprecated since Twig 3.9.0
+ */
+function twig_template_from_string(Environment $env, $template, string $name = null): TemplateWrapper
+{
+    trigger_deprecation('twig/twig', '3.9.0', 'Using the internal "%s" function is deprecated.', __FUNCTION__);
+
+    return StringLoaderExtension::templateFromString($env, $template, $name);
+}
diff --git a/tests/Extension/LegacyStringLoaderFunctionsTest.php b/tests/Extension/LegacyStringLoaderFunctionsTest.php
new file mode 100644
index 000000000..a6cb31df0
--- /dev/null
+++ b/tests/Extension/LegacyStringLoaderFunctionsTest.php
@@ -0,0 +1,30 @@
+<?php
+
+/*
+ * This file is part of Twig.
+ *
+ * (c) Fabien Potencier
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Twig\Tests\Extension;
+
+use PHPUnit\Framework\TestCase;
+use Twig\Environment;
+use Twig\Extension\StringLoaderExtension;
+use Twig\Loader\ArrayLoader;
+
+/**
+ * @group legacy
+ */
+class LegacyStringLoaderFunctionsTest extends TestCase
+{
+    public function testTemplateFromString()
+    {
+        $env = new Environment(new ArrayLoader());
+
+        $this->assertSame(StringLoaderExtension::templateFromString($env, 'Foo')->render(), twig_template_from_string($env, 'Foo')->render());
+    }
+}
diff --git a/tests/Extension/StringLoaderExtensionTest.php b/tests/Extension/StringLoaderExtensionTest.php
index 363a0825e..e4fa2e3ba 100644
--- a/tests/Extension/StringLoaderExtensionTest.php
+++ b/tests/Extension/StringLoaderExtensionTest.php
@@ -21,6 +21,6 @@ class StringLoaderExtensionTest extends TestCase
     {
         $twig = new Environment($this->createMock('\Twig\Loader\LoaderInterface'));
         $twig->addExtension(new StringLoaderExtension());
-        $this->assertSame('something', twig_include($twig, [], twig_template_from_string($twig, 'something')));
+        $this->assertSame('something', twig_include($twig, [], StringLoaderExtension::templateFromString($twig, 'something')));
     }
 }