diff --git a/.travis.yml b/.travis.yml
index 19f2186295..e1490ca203 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -22,7 +22,6 @@ env:
         - MESSENGER_AMQP_DSN=amqp://localhost/%2f/messages
         - MESSENGER_REDIS_DSN=redis://127.0.0.1:7001/messages
         - SYMFONY_PHPUNIT_DISABLE_RESULT_CACHE=1
-        - SYMFONY_PATCH_TYPE_DECLARATIONS=force=0
 
 matrix:
     include:
@@ -299,9 +298,8 @@ install:
                   ln -sd $(realpath src/Symfony/Contracts) vendor/symfony/contracts
                   sed -i 's/"\*\*\/Tests\/"//' composer.json
                   composer install --optimize-autoloader
-                  export SYMFONY_PATCH_TYPE_DECLARATIONS=force=object
-                  php .github/patch-types.php
-                  php .github/patch-types.php # ensure the script is idempotent
+                  SYMFONY_PATCH_TYPE_DECLARATIONS=force=object php .github/patch-types.php
+                  SYMFONY_PATCH_TYPE_DECLARATIONS=force=object php .github/patch-types.php # ensure the script is idempotent
                   PHPUNIT_X="$PHPUNIT_X,legacy"
               fi
 
diff --git a/phpunit b/phpunit
index b885570d65..a0f1af86d7 100755
--- a/phpunit
+++ b/phpunit
@@ -14,5 +14,8 @@ if (!getenv('SYMFONY_PHPUNIT_VERSION')) {
         putenv('SYMFONY_PHPUNIT_VERSION=6.5');
     }
 }
+if (!getenv('SYMFONY_PATCH_TYPE_DECLARATIONS')) {
+    putenv('SYMFONY_PATCH_TYPE_DECLARATIONS=deprecations=1');
+}
 putenv('SYMFONY_PHPUNIT_DIR='.__DIR__.'/.phpunit');
 require __DIR__.'/vendor/symfony/phpunit-bridge/bin/simple-phpunit';
diff --git a/src/Symfony/Component/ErrorHandler/DebugClassLoader.php b/src/Symfony/Component/ErrorHandler/DebugClassLoader.php
index 6d9239c5ac..a09d8d57c6 100644
--- a/src/Symfony/Component/ErrorHandler/DebugClassLoader.php
+++ b/src/Symfony/Component/ErrorHandler/DebugClassLoader.php
@@ -27,11 +27,14 @@ use ProxyManager\Proxy\ProxyInterface;
  * It can also patch classes to turn docblocks into actual return types.
  * This behavior is controlled by the SYMFONY_PATCH_TYPE_DECLARATIONS env var,
  * which is a url-encoded array with the follow parameters:
- *  - force: any value enables deprecation notices - can be any of:
+ *  - "force": any value enables deprecation notices - can be any of:
  *      - "docblock" to patch only docblock annotations
  *      - "object" to turn union types to the "object" type when possible (not recommended)
- *      - "1"/"0" to enable/disable patching of return types
- *  - php: the target version of PHP - e.g. "7.1" doesn't generate "object" types
+ *      - "1" to add all possible return types including magic methods
+ *      - "0" to add possible return types excluding magic methods
+ *  - "php": the target version of PHP - e.g. "7.1" doesn't generate "object" types
+ *  - "deprecations": "1" to trigger a deprecation notice when a child class misses a
+ *                    return type while the parent declares an "@return" annotation
  *
  * Note that patching doesn't care about any coding style so you'd better to run
  * php-cs-fixer after, with rules "phpdoc_trim_consecutive_blank_line_separation"
@@ -177,6 +180,7 @@ class DebugClassLoader
         $this->patchTypes += [
             'force' => null,
             'php' => null,
+            'deprecations' => false,
         ];
 
         if (!isset(self::$caseCheck)) {
@@ -571,7 +575,7 @@ class DebugClassLoader
 
             $forcePatchTypes = $this->patchTypes['force'];
 
-            if ($canAddReturnType = $forcePatchTypes && false === strpos($method->getFileName(), \DIRECTORY_SEPARATOR.'vendor'.\DIRECTORY_SEPARATOR)) {
+            if ($canAddReturnType = null !== $forcePatchTypes && false === strpos($method->getFileName(), \DIRECTORY_SEPARATOR.'vendor'.\DIRECTORY_SEPARATOR)) {
                 if ('void' !== (self::MAGIC_METHODS[$method->name] ?? 'void')) {
                     $this->patchTypes['force'] = $forcePatchTypes ?: 'docblock';
                 }
@@ -600,7 +604,7 @@ class DebugClassLoader
                 if (strncmp($ns, $declaringClass, $len)) {
                     if ($canAddReturnType && 'docblock' === $this->patchTypes['force'] && false === strpos($method->getFileName(), \DIRECTORY_SEPARATOR.'vendor'.\DIRECTORY_SEPARATOR)) {
                         $this->patchMethod($method, $returnType, $declaringFile, $normalizedType);
-                    } elseif ('' !== $declaringClass && null !== $this->patchTypes['force']) {
+                    } elseif ('' !== $declaringClass && $this->patchTypes['deprecations']) {
                         $deprecations[] = sprintf('Method "%s::%s()" will return "%s" as of its next major version. Doing the same in child class "%s" will be required when upgrading.', $declaringClass, $method->name, $normalizedType, $className);
                     }
                 }
diff --git a/src/Symfony/Component/ErrorHandler/Tests/DebugClassLoaderTest.php b/src/Symfony/Component/ErrorHandler/Tests/DebugClassLoaderTest.php
index 99bb28cd56..4731f2a2db 100644
--- a/src/Symfony/Component/ErrorHandler/Tests/DebugClassLoaderTest.php
+++ b/src/Symfony/Component/ErrorHandler/Tests/DebugClassLoaderTest.php
@@ -24,7 +24,7 @@ class DebugClassLoaderTest extends TestCase
     {
         $this->patchTypes = getenv('SYMFONY_PATCH_TYPE_DECLARATIONS');
         $this->errorReporting = error_reporting(E_ALL);
-        putenv('SYMFONY_PATCH_TYPE_DECLARATIONS=force=0');
+        putenv('SYMFONY_PATCH_TYPE_DECLARATIONS=deprecations=1');
         $this->loader = [new DebugClassLoader([new ClassLoader(), 'loadClass']), 'loadClass'];
         spl_autoload_register($this->loader, true, true);
     }