diff --git a/UPGRADE-5.1.md b/UPGRADE-5.1.md
index c2f4910726..fed8562658 100644
--- a/UPGRADE-5.1.md
+++ b/UPGRADE-5.1.md
@@ -6,6 +6,11 @@ Console
 
  * `Command::setHidden()` is final since Symfony 5.1
 
+Dotenv
+------
+
+ * Deprecated passing `$usePutenv` argument to Dotenv's constructor, use `Dotenv::usePutenv()` instead.
+
 EventDispatcher
 ---------------
 
diff --git a/UPGRADE-6.0.md b/UPGRADE-6.0.md
index 8ff5ab2491..d5908b9084 100644
--- a/UPGRADE-6.0.md
+++ b/UPGRADE-6.0.md
@@ -6,6 +6,11 @@ Console
 
  * `Command::setHidden()` has a default value (`true`) for `$hidden` parameter
 
+Dotenv
+------
+
+ * Removed argument `$usePutenv` from Dotenv's constructor, use `Dotenv::usePutenv()` instead.
+
 EventDispatcher
 ---------------
 
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Secrets/DotenvVaultTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Secrets/DotenvVaultTest.php
index d494c82e68..62ca08b07c 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Secrets/DotenvVaultTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Secrets/DotenvVaultTest.php
@@ -38,7 +38,7 @@ class DotenvVaultTest extends TestCase
         $vault->seal('foo', $plain);
 
         unset($_SERVER['foo'], $_ENV['foo']);
-        (new Dotenv(false))->load($this->envFile);
+        (new Dotenv())->load($this->envFile);
 
         $decrypted = $vault->reveal('foo');
         $this->assertSame($plain, $decrypted);
@@ -50,7 +50,7 @@ class DotenvVaultTest extends TestCase
         $this->assertFalse($vault->remove('foo'));
 
         unset($_SERVER['foo'], $_ENV['foo']);
-        (new Dotenv(false))->load($this->envFile);
+        (new Dotenv())->load($this->envFile);
 
         $this->assertArrayNotHasKey('foo', $vault->list());
     }
diff --git a/src/Symfony/Bundle/FrameworkBundle/composer.json b/src/Symfony/Bundle/FrameworkBundle/composer.json
index 896d149b10..ac3ce7572b 100644
--- a/src/Symfony/Bundle/FrameworkBundle/composer.json
+++ b/src/Symfony/Bundle/FrameworkBundle/composer.json
@@ -37,7 +37,7 @@
         "symfony/console": "^4.4|^5.0",
         "symfony/css-selector": "^4.4|^5.0",
         "symfony/dom-crawler": "^4.4|^5.0",
-        "symfony/dotenv": "^4.4|^5.0",
+        "symfony/dotenv": "^5.1",
         "symfony/polyfill-intl-icu": "~1.0",
         "symfony/form": "^4.4|^5.0",
         "symfony/expression-language": "^4.4|^5.0",
@@ -71,7 +71,7 @@
         "symfony/asset": "<4.4",
         "symfony/browser-kit": "<4.4",
         "symfony/console": "<4.4",
-        "symfony/dotenv": "<4.4",
+        "symfony/dotenv": "<5.1",
         "symfony/dom-crawler": "<4.4",
         "symfony/http-client": "<4.4",
         "symfony/form": "<4.4",
diff --git a/src/Symfony/Component/Console/composer.json b/src/Symfony/Component/Console/composer.json
index 34cb029543..ee1d76f6c2 100644
--- a/src/Symfony/Component/Console/composer.json
+++ b/src/Symfony/Component/Console/composer.json
@@ -41,6 +41,7 @@
     },
     "conflict": {
         "symfony/dependency-injection": "<4.4",
+        "symfony/dotenv": "<5.1",
         "symfony/event-dispatcher": "<4.4",
         "symfony/lock": "<4.4",
         "symfony/process": "<4.4"
diff --git a/src/Symfony/Component/Dotenv/CHANGELOG.md b/src/Symfony/Component/Dotenv/CHANGELOG.md
index ef1df04aee..e004ed8d75 100644
--- a/src/Symfony/Component/Dotenv/CHANGELOG.md
+++ b/src/Symfony/Component/Dotenv/CHANGELOG.md
@@ -1,6 +1,15 @@
 CHANGELOG
 =========
 
+5.1.0
+-----
+
+ * added `Dotenv::bootEnv()` to check for `.env.local.php` before calling `Dotenv::loadEnv()`
+ * added `Dotenv::setProdEnvs()` and `Dotenv::usePutenv()`
+ * made Dotenv's constructor accept `$envKey` and `$debugKey` arguments, to define
+   the name of the env vars that configure the env name and debug settings
+ * deprecated passing `$usePutenv` argument to Dotenv's constructor
+
 5.0.0
 -----
 
diff --git a/src/Symfony/Component/Dotenv/Dotenv.php b/src/Symfony/Component/Dotenv/Dotenv.php
index 8851514451..596117b90b 100644
--- a/src/Symfony/Component/Dotenv/Dotenv.php
+++ b/src/Symfony/Component/Dotenv/Dotenv.php
@@ -35,15 +35,47 @@ final class Dotenv
     private $data;
     private $end;
     private $values;
-    private $usePutenv;
+    private $envKey;
+    private $debugKey;
+    private $prodEnvs = ['prod'];
+    private $usePutenv = false;
 
     /**
-     * @var bool If `putenv()` should be used to define environment variables or not.
-     *           Beware that `putenv()` is not thread safe, that's why this setting defaults to false
+     * @param string $envKey
      */
-    public function __construct(bool $usePutenv = false)
+    public function __construct($envKey = 'APP_ENV', string $debugKey = 'APP_DEBUG')
+    {
+        if (\in_array($envKey = (string) $envKey, ['1', ''], true)) {
+            @trigger_error(sprintf('Passing a boolean to the constructor of "%s" is deprecated since Symfony 5.1, use "Dotenv::usePutenv()".', __CLASS__), E_USER_DEPRECATED);
+            $this->usePutenv = (bool) $envKey;
+            $envKey = 'APP_ENV';
+        }
+
+        $this->envKey = $envKey;
+        $this->debugKey = $debugKey;
+    }
+
+    /**
+     * @return $this
+     */
+    public function setProdEnvs(array $prodEnvs): self
+    {
+        $this->prodEnvs = $prodEnvs;
+
+        return $this;
+    }
+
+    /**
+     * @param bool $usePutenv If `putenv()` should be used to define environment variables or not.
+     *                        Beware that `putenv()` is not thread safe, that's why this setting defaults to false
+     *
+     * @return $this
+     */
+    public function usePutenv($usePutenv = true): self
     {
         $this->usePutenv = $usePutenv;
+
+        return $this;
     }
 
     /**
@@ -66,29 +98,31 @@ final class Dotenv
      * .env.local is always ignored in test env because tests should produce the same results for everyone.
      * .env.dist is loaded when it exists and .env is not found.
      *
-     * @param string $path       A file to load
-     * @param string $varName    The name of the env vars that defines the app env
-     * @param string $defaultEnv The app env to use when none is defined
-     * @param array  $testEnvs   A list of app envs for which .env.local should be ignored
+     * @param string $path        A file to load
+     * @param string $envKey|null The name of the env vars that defines the app env
+     * @param string $defaultEnv  The app env to use when none is defined
+     * @param array  $testEnvs    A list of app envs for which .env.local should be ignored
      *
      * @throws FormatException when a file has a syntax error
      * @throws PathException   when a file does not exist or is not readable
      */
-    public function loadEnv(string $path, string $varName = 'APP_ENV', string $defaultEnv = 'dev', array $testEnvs = ['test']): void
+    public function loadEnv(string $path, string $envKey = null, string $defaultEnv = 'dev', array $testEnvs = ['test']): void
     {
+        $k = $envKey ?? $this->envKey;
+
         if (file_exists($path) || !file_exists($p = "$path.dist")) {
             $this->load($path);
         } else {
             $this->load($p);
         }
 
-        if (null === $env = $_SERVER[$varName] ?? $_ENV[$varName] ?? null) {
-            $this->populate([$varName => $env = $defaultEnv]);
+        if (null === $env = $_SERVER[$k] ?? $_ENV[$k] ?? null) {
+            $this->populate([$k => $env = $defaultEnv]);
         }
 
         if (!\in_array($env, $testEnvs, true) && file_exists($p = "$path.local")) {
             $this->load($p);
-            $env = $_SERVER[$varName] ?? $_ENV[$varName] ?? $env;
+            $env = $_SERVER[$k] ?? $_ENV[$k] ?? $env;
         }
 
         if ('local' === $env) {
@@ -104,6 +138,32 @@ final class Dotenv
         }
     }
 
+    /**
+     * Loads env vars from .env.local.php if the file exists or from the other .env files otherwise.
+     *
+     * This method also configures the APP_DEBUG env var according to the current APP_ENV.
+     *
+     * See method loadEnv() for rules related to .env files.
+     */
+    public function bootEnv(string $path, string $defaultEnv = 'dev', array $testEnvs = ['test']): void
+    {
+        $p = $path.'.local.php';
+        $env = (\function_exists('opcache_is_script_cached') && @opcache_is_script_cached($p)) || file_exists($p) ? include $p : null;
+        $k = $this->envKey;
+
+        if (\is_array($env) && (!isset($env[$k]) || ($_SERVER[$k] ?? $_ENV[$k] ?? $env[$k]) === $env[$k])) {
+            $this->populate($env);
+        } else {
+            $this->loadEnv($path, $k, $defaultEnv, $testEnvs);
+        }
+
+        $_SERVER += $_ENV;
+
+        $k = $this->debugKey;
+        $debug = $_SERVER[$k] ?? !\in_array($_SERVER[$this->envKey], $this->prodEnvs, true);
+        $_SERVER[$k] = $_ENV[$k] = (int) $debug || (!\is_bool($debug) && filter_var($debug, FILTER_VALIDATE_BOOLEAN)) ? '1' : '0';
+    }
+
     /**
      * Loads one or several .env files and enables override existing vars.
      *
diff --git a/src/Symfony/Component/Dotenv/Tests/DotenvTest.php b/src/Symfony/Component/Dotenv/Tests/DotenvTest.php
index 1ae3eefa94..f43ebac6ac 100644
--- a/src/Symfony/Component/Dotenv/Tests/DotenvTest.php
+++ b/src/Symfony/Component/Dotenv/Tests/DotenvTest.php
@@ -22,7 +22,7 @@ class DotenvTest extends TestCase
      */
     public function testParseWithFormatError($data, $error)
     {
-        $dotenv = new Dotenv(true);
+        $dotenv = new Dotenv();
 
         try {
             $dotenv->parse($data);
@@ -66,7 +66,7 @@ class DotenvTest extends TestCase
      */
     public function testParse($data, $expected)
     {
-        $dotenv = new Dotenv(true);
+        $dotenv = new Dotenv();
         $this->assertSame($expected, $dotenv->parse($data));
     }
 
@@ -208,7 +208,7 @@ class DotenvTest extends TestCase
         file_put_contents($path1, 'FOO=BAR');
         file_put_contents($path2, 'BAR=BAZ');
 
-        (new Dotenv(true))->load($path1, $path2);
+        (new Dotenv())->usePutenv()->load($path1, $path2);
 
         $foo = getenv('FOO');
         $bar = getenv('BAR');
@@ -239,7 +239,7 @@ class DotenvTest extends TestCase
         // .env
 
         file_put_contents($path, 'FOO=BAR');
-        (new Dotenv(true))->loadEnv($path, 'TEST_APP_ENV');
+        (new Dotenv())->usePutenv()->loadEnv($path, 'TEST_APP_ENV');
         $this->assertSame('BAR', getenv('FOO'));
         $this->assertSame('dev', getenv('TEST_APP_ENV'));
 
@@ -247,33 +247,33 @@ class DotenvTest extends TestCase
 
         $_SERVER['TEST_APP_ENV'] = 'local';
         file_put_contents("$path.local", 'FOO=localBAR');
-        (new Dotenv(true))->loadEnv($path, 'TEST_APP_ENV');
+        (new Dotenv())->usePutenv()->loadEnv($path, 'TEST_APP_ENV');
         $this->assertSame('localBAR', getenv('FOO'));
 
         // special case for test
 
         $_SERVER['TEST_APP_ENV'] = 'test';
-        (new Dotenv(true))->loadEnv($path, 'TEST_APP_ENV');
+        (new Dotenv())->usePutenv()->loadEnv($path, 'TEST_APP_ENV');
         $this->assertSame('BAR', getenv('FOO'));
 
         // .env.dev
 
         unset($_SERVER['TEST_APP_ENV']);
         file_put_contents("$path.dev", 'FOO=devBAR');
-        (new Dotenv(true))->loadEnv($path, 'TEST_APP_ENV');
+        (new Dotenv())->usePutenv()->loadEnv($path, 'TEST_APP_ENV');
         $this->assertSame('devBAR', getenv('FOO'));
 
         // .env.dev.local
 
         file_put_contents("$path.dev.local", 'FOO=devlocalBAR');
-        (new Dotenv(true))->loadEnv($path, 'TEST_APP_ENV');
+        (new Dotenv())->usePutenv()->loadEnv($path, 'TEST_APP_ENV');
         $this->assertSame('devlocalBAR', getenv('FOO'));
 
         // .env.dist
 
         unlink($path);
         file_put_contents("$path.dist", 'BAR=distBAR');
-        (new Dotenv(true))->loadEnv($path, 'TEST_APP_ENV');
+        (new Dotenv())->usePutenv()->loadEnv($path, 'TEST_APP_ENV');
         $this->assertSame('distBAR', getenv('BAR'));
 
         putenv('FOO');
@@ -305,7 +305,7 @@ class DotenvTest extends TestCase
         file_put_contents($path1, 'FOO=BAR');
         file_put_contents($path2, 'BAR=BAZ');
 
-        (new Dotenv(true))->overload($path1, $path2);
+        (new Dotenv())->usePutenv()->overload($path1, $path2);
 
         $foo = getenv('FOO');
         $bar = getenv('BAR');
@@ -323,7 +323,7 @@ class DotenvTest extends TestCase
     public function testLoadDirectory()
     {
         $this->expectException('Symfony\Component\Dotenv\Exception\PathException');
-        $dotenv = new Dotenv(true);
+        $dotenv = new Dotenv();
         $dotenv->load(__DIR__);
     }
 
@@ -331,7 +331,7 @@ class DotenvTest extends TestCase
     {
         $originalValue = $_SERVER['argc'];
 
-        $dotenv = new Dotenv(true);
+        $dotenv = new Dotenv();
         $dotenv->populate(['argc' => 'new_value']);
 
         $this->assertSame($originalValue, $_SERVER['argc']);
@@ -342,7 +342,7 @@ class DotenvTest extends TestCase
         putenv('TEST_ENV_VAR=original_value');
         $_SERVER['TEST_ENV_VAR'] = 'original_value';
 
-        $dotenv = new Dotenv(true);
+        $dotenv = (new Dotenv())->usePutenv();
         $dotenv->populate(['TEST_ENV_VAR' => 'new_value']);
 
         $this->assertSame('original_value', getenv('TEST_ENV_VAR'));
@@ -352,7 +352,7 @@ class DotenvTest extends TestCase
     {
         $_SERVER['HTTP_TEST_ENV_VAR'] = 'http_value';
 
-        $dotenv = new Dotenv(true);
+        $dotenv = (new Dotenv())->usePutenv();
         $dotenv->populate(['HTTP_TEST_ENV_VAR' => 'env_value']);
 
         $this->assertSame('env_value', getenv('HTTP_TEST_ENV_VAR'));
@@ -364,7 +364,7 @@ class DotenvTest extends TestCase
     {
         putenv('TEST_ENV_VAR_OVERRIDEN=original_value');
 
-        $dotenv = new Dotenv(true);
+        $dotenv = (new Dotenv())->usePutenv();
         $dotenv->populate(['TEST_ENV_VAR_OVERRIDEN' => 'new_value'], true);
 
         $this->assertSame('new_value', getenv('TEST_ENV_VAR_OVERRIDEN'));
@@ -386,7 +386,7 @@ class DotenvTest extends TestCase
         unset($_SERVER['DATABASE_URL']);
         putenv('DATABASE_URL');
 
-        $dotenv = new Dotenv(true);
+        $dotenv = (new Dotenv())->usePutenv();
         $dotenv->populate(['APP_DEBUG' => '1', 'DATABASE_URL' => 'mysql://root@localhost/db']);
 
         $this->assertSame('APP_DEBUG,DATABASE_URL', getenv('SYMFONY_DOTENV_VARS'));
@@ -403,7 +403,7 @@ class DotenvTest extends TestCase
         unset($_SERVER['DATABASE_URL']);
         putenv('DATABASE_URL');
 
-        $dotenv = new Dotenv(true);
+        $dotenv = (new Dotenv())->usePutenv();
         $dotenv->populate(['APP_DEBUG' => '0', 'DATABASE_URL' => 'mysql://root@localhost/db']);
         $dotenv->populate(['DATABASE_URL' => 'sqlite:///somedb.sqlite']);
 
@@ -419,7 +419,7 @@ class DotenvTest extends TestCase
         putenv('BAZ=baz');
         putenv('DOCUMENT_ROOT=/var/www');
 
-        $dotenv = new Dotenv(true);
+        $dotenv = (new Dotenv())->usePutenv();
         $dotenv->populate(['FOO' => 'foo1', 'BAR' => 'bar1', 'BAZ' => 'baz1', 'DOCUMENT_ROOT' => '/boot']);
 
         $this->assertSame('foo1', getenv('FOO'));
@@ -431,7 +431,7 @@ class DotenvTest extends TestCase
     public function testGetVariablesValueFromEnvFirst()
     {
         $_ENV['APP_ENV'] = 'prod';
-        $dotenv = new Dotenv(true);
+        $dotenv = new Dotenv();
 
         $test = "APP_ENV=dev\nTEST1=foo1_\${APP_ENV}";
         $values = $dotenv->parse($test);
@@ -448,7 +448,7 @@ class DotenvTest extends TestCase
     {
         putenv('Foo=Bar');
 
-        $dotenv = new Dotenv(true);
+        $dotenv = new Dotenv();
 
         try {
             $values = $dotenv->parse('Foo=${Foo}');
@@ -460,19 +460,40 @@ class DotenvTest extends TestCase
 
     public function testNoDeprecationWarning()
     {
-        $dotenv = new Dotenv(true);
-        $this->assertInstanceOf(Dotenv::class, $dotenv);
-        $dotenv = new Dotenv(false);
+        $dotenv = new Dotenv();
         $this->assertInstanceOf(Dotenv::class, $dotenv);
     }
 
     public function testDoNotUsePutenv()
     {
-        $dotenv = new Dotenv(false);
+        $dotenv = new Dotenv();
         $dotenv->populate(['TEST_USE_PUTENV' => 'no']);
 
         $this->assertSame('no', $_SERVER['TEST_USE_PUTENV']);
         $this->assertSame('no', $_ENV['TEST_USE_PUTENV']);
         $this->assertFalse(getenv('TEST_USE_PUTENV'));
     }
+
+    public function testBootEnv()
+    {
+        @mkdir($tmpdir = sys_get_temp_dir().'/dotenv');
+        $path = tempnam($tmpdir, 'sf-');
+
+        file_put_contents($path, 'FOO=BAR');
+        (new Dotenv('TEST_APP_ENV', 'TEST_APP_DEBUG'))->bootEnv($path);
+
+        $this->assertSame('BAR', $_SERVER['FOO']);
+
+        unset($_SERVER['FOO'], $_ENV['FOO']);
+        unlink($path);
+
+        file_put_contents($path.'.local.php', '<?php return ["TEST_APP_ENV" => "dev", "FOO" => "BAR"];');
+        (new Dotenv('TEST_APP_ENV', 'TEST_APP_DEBUG'))->bootEnv($path);
+        $this->assertSame('BAR', $_SERVER['FOO']);
+        $this->assertSame('1', $_SERVER['TEST_APP_DEBUG']);
+
+        unset($_SERVER['FOO'], $_ENV['FOO']);
+        unlink($path.'.local.php');
+        rmdir($tmpdir);
+    }
 }