diff --git a/Definition/ArrayNode.php b/Definition/ArrayNode.php
index 83bab205e..59a0af879 100644
--- a/Definition/ArrayNode.php
+++ b/Definition/ArrayNode.php
@@ -235,7 +235,7 @@ protected function finalizeValue($value)
             }
 
             if ($child->isDeprecated()) {
-                @trigger_error($child->getDeprecationMessage($name, $this->getPath()), E_USER_DEPRECATED);
+                @trigger_error($child->getDeprecationMessage($name, $this->getPath()), \E_USER_DEPRECATED);
             }
 
             try {
diff --git a/Definition/Builder/ArrayNodeDefinition.php b/Definition/Builder/ArrayNodeDefinition.php
index 29d1e154f..da4ebf627 100644
--- a/Definition/Builder/ArrayNodeDefinition.php
+++ b/Definition/Builder/ArrayNodeDefinition.php
@@ -413,7 +413,7 @@ protected function createNode()
             }
 
             if (false === $this->allowEmptyValue) {
-                @trigger_error(sprintf('Using %s::cannotBeEmpty() at path "%s" has no effect, consider requiresAtLeastOneElement() instead. In 4.0 both methods will behave the same.', __CLASS__, $node->getPath()), E_USER_DEPRECATED);
+                @trigger_error(sprintf('Using %s::cannotBeEmpty() at path "%s" has no effect, consider requiresAtLeastOneElement() instead. In 4.0 both methods will behave the same.', __CLASS__, $node->getPath()), \E_USER_DEPRECATED);
             }
 
             if (true === $this->atLeastOne) {
@@ -476,7 +476,7 @@ protected function validateConcreteNode(ArrayNode $node)
         }
 
         if (false === $this->allowEmptyValue) {
-            @trigger_error(sprintf('->cannotBeEmpty() is not applicable to concrete nodes at path "%s". In 4.0 it will throw an exception.', $path), E_USER_DEPRECATED);
+            @trigger_error(sprintf('->cannotBeEmpty() is not applicable to concrete nodes at path "%s". In 4.0 it will throw an exception.', $path), \E_USER_DEPRECATED);
         }
 
         if (true === $this->atLeastOne) {
diff --git a/Definition/Dumper/XmlReferenceDumper.php b/Definition/Dumper/XmlReferenceDumper.php
index 744f15fd8..7f8639908 100644
--- a/Definition/Dumper/XmlReferenceDumper.php
+++ b/Definition/Dumper/XmlReferenceDumper.php
@@ -193,7 +193,7 @@ private function writeNode(NodeInterface $node, $depth = 0, $root = false, $name
                 $commentDepth = $depth + 4 + \strlen($attrName) + 2;
                 $commentLines = explode("\n", $comment);
                 $multiline = (\count($commentLines) > 1);
-                $comment = implode(PHP_EOL.str_repeat(' ', $commentDepth), $commentLines);
+                $comment = implode(\PHP_EOL.str_repeat(' ', $commentDepth), $commentLines);
 
                 if ($multiline) {
                     $this->writeLine('<!--', $depth);
@@ -267,7 +267,7 @@ private function writeLine($text, $indent = 0)
         $indent = \strlen($text) + $indent;
         $format = '%'.$indent.'s';
 
-        $this->reference .= sprintf($format, $text).PHP_EOL;
+        $this->reference .= sprintf($format, $text).\PHP_EOL;
     }
 
     /**
diff --git a/DependencyInjection/ConfigCachePass.php b/DependencyInjection/ConfigCachePass.php
index 128bf7e28..30df15be8 100644
--- a/DependencyInjection/ConfigCachePass.php
+++ b/DependencyInjection/ConfigCachePass.php
@@ -11,7 +11,7 @@
 
 namespace Symfony\Component\Config\DependencyInjection;
 
-@trigger_error(sprintf('The %s class is deprecated since Symfony 3.4 and will be removed in 4.0. Use tagged iterator arguments instead.', ConfigCachePass::class), E_USER_DEPRECATED);
+@trigger_error(sprintf('The %s class is deprecated since Symfony 3.4 and will be removed in 4.0. Use tagged iterator arguments instead.', ConfigCachePass::class), \E_USER_DEPRECATED);
 
 use Symfony\Component\DependencyInjection\Argument\IteratorArgument;
 use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
diff --git a/FileLocator.php b/FileLocator.php
index c125ba0b1..5f315ba72 100644
--- a/FileLocator.php
+++ b/FileLocator.php
@@ -88,7 +88,7 @@ private function isAbsolutePath($file)
                 && ':' === $file[1]
                 && ('\\' === $file[2] || '/' === $file[2])
             )
-            || null !== parse_url($file, PHP_URL_SCHEME)
+            || null !== parse_url($file, \PHP_URL_SCHEME)
         ) {
             return true;
         }
diff --git a/Resource/GlobResource.php b/Resource/GlobResource.php
index 13d2ee7d7..1aa3bcf69 100644
--- a/Resource/GlobResource.php
+++ b/Resource/GlobResource.php
@@ -100,7 +100,7 @@ public function getIterator()
         }
 
         if (0 !== strpos($this->prefix, 'phar://') && false === strpos($this->pattern, '/**/') && (\defined('GLOB_BRACE') || false === strpos($this->pattern, '{'))) {
-            $paths = glob($this->prefix.$this->pattern, GLOB_NOSORT | (\defined('GLOB_BRACE') ? GLOB_BRACE : 0));
+            $paths = glob($this->prefix.$this->pattern, \GLOB_NOSORT | (\defined('GLOB_BRACE') ? \GLOB_BRACE : 0));
             sort($paths);
             foreach ($paths as $path) {
                 if ($this->recursive && is_dir($path)) {
diff --git a/ResourceCheckerConfigCache.php b/ResourceCheckerConfigCache.php
index 092b95bf0..0538f3f44 100644
--- a/ResourceCheckerConfigCache.php
+++ b/ResourceCheckerConfigCache.php
@@ -137,7 +137,7 @@ public function write($content, array $metadata = null)
             }
         }
 
-        if (\function_exists('opcache_invalidate') && filter_var(ini_get('opcache.enable'), FILTER_VALIDATE_BOOLEAN)) {
+        if (\function_exists('opcache_invalidate') && filter_var(ini_get('opcache.enable'), \FILTER_VALIDATE_BOOLEAN)) {
             @opcache_invalidate($this->file, true);
         }
     }
diff --git a/Tests/Definition/ArrayNodeTest.php b/Tests/Definition/ArrayNodeTest.php
index 25c2cfc69..f726e8dd0 100644
--- a/Tests/Definition/ArrayNodeTest.php
+++ b/Tests/Definition/ArrayNodeTest.php
@@ -216,7 +216,7 @@ public function testSetDeprecated()
 
         $deprecationTriggered = false;
         $deprecationHandler = function ($level, $message, $file, $line) use (&$prevErrorHandler, &$deprecationTriggered) {
-            if (E_USER_DEPRECATED === $level) {
+            if (\E_USER_DEPRECATED === $level) {
                 return $deprecationTriggered = true;
             }
 
diff --git a/Tests/Definition/Dumper/XmlReferenceDumperTest.php b/Tests/Definition/Dumper/XmlReferenceDumperTest.php
index 5bc961bab..1bd60215d 100644
--- a/Tests/Definition/Dumper/XmlReferenceDumperTest.php
+++ b/Tests/Definition/Dumper/XmlReferenceDumperTest.php
@@ -35,7 +35,7 @@ public function testNamespaceDumper()
 
     private function getConfigurationAsString()
     {
-        return str_replace("\n", PHP_EOL, <<<'EOL'
+        return str_replace("\n", \PHP_EOL, <<<'EOL'
 <!-- Namespace: http://example.org/schema/dic/acme_root -->
 <!-- scalar-required: Required -->
 <!-- scalar-deprecated: Deprecated (The child node "scalar_deprecated" at path "acme_root" is deprecated.) -->
diff --git a/Tests/Definition/ScalarNodeTest.php b/Tests/Definition/ScalarNodeTest.php
index 4413baf3c..ac2d9376f 100644
--- a/Tests/Definition/ScalarNodeTest.php
+++ b/Tests/Definition/ScalarNodeTest.php
@@ -54,7 +54,7 @@ public function testSetDeprecated()
 
         $deprecationTriggered = 0;
         $deprecationHandler = function ($level, $message, $file, $line) use (&$prevErrorHandler, &$deprecationTriggered) {
-            if (E_USER_DEPRECATED === $level) {
+            if (\E_USER_DEPRECATED === $level) {
                 return ++$deprecationTriggered;
             }
 
diff --git a/Tests/Loader/LoaderTest.php b/Tests/Loader/LoaderTest.php
index 35a911ef3..79ddf00f6 100644
--- a/Tests/Loader/LoaderTest.php
+++ b/Tests/Loader/LoaderTest.php
@@ -107,7 +107,7 @@ public function load($resource, $type = null)
 
     public function supports($resource, $type = null)
     {
-        return \is_string($resource) && 'foo' === pathinfo($resource, PATHINFO_EXTENSION);
+        return \is_string($resource) && 'foo' === pathinfo($resource, \PATHINFO_EXTENSION);
     }
 
     public function getType()
diff --git a/Tests/Util/XmlUtilsTest.php b/Tests/Util/XmlUtilsTest.php
index a82e939d9..f0b77ae6f 100644
--- a/Tests/Util/XmlUtilsTest.php
+++ b/Tests/Util/XmlUtilsTest.php
@@ -199,7 +199,7 @@ public function testLoadEmptyXmlFile()
     // test for issue https://github.com/symfony/symfony/issues/9731
     public function testLoadWrongEmptyXMLWithErrorHandler()
     {
-        if (LIBXML_VERSION < 20900) {
+        if (\LIBXML_VERSION < 20900) {
             $originalDisableEntities = libxml_disable_entity_loader(false);
         }
         $errorReporting = error_reporting(-1);
@@ -221,7 +221,7 @@ public function testLoadWrongEmptyXMLWithErrorHandler()
             error_reporting($errorReporting);
         }
 
-        if (LIBXML_VERSION < 20900) {
+        if (\LIBXML_VERSION < 20900) {
             $disableEntities = libxml_disable_entity_loader(true);
             libxml_disable_entity_loader($disableEntities);
 
diff --git a/Util/XmlUtils.php b/Util/XmlUtils.php
index 203741ad1..d833c428e 100644
--- a/Util/XmlUtils.php
+++ b/Util/XmlUtils.php
@@ -51,15 +51,15 @@ public static function parse($content, $schemaOrCallable = null)
         }
 
         $internalErrors = libxml_use_internal_errors(true);
-        if (LIBXML_VERSION < 20900) {
+        if (\LIBXML_VERSION < 20900) {
             $disableEntities = libxml_disable_entity_loader(true);
         }
         libxml_clear_errors();
 
         $dom = new \DOMDocument();
         $dom->validateOnParse = true;
-        if (!$dom->loadXML($content, LIBXML_NONET | (\defined('LIBXML_COMPACT') ? LIBXML_COMPACT : 0))) {
-            if (LIBXML_VERSION < 20900) {
+        if (!$dom->loadXML($content, \LIBXML_NONET | (\defined('LIBXML_COMPACT') ? \LIBXML_COMPACT : 0))) {
+            if (\LIBXML_VERSION < 20900) {
                 libxml_disable_entity_loader($disableEntities);
             }
 
@@ -69,12 +69,12 @@ public static function parse($content, $schemaOrCallable = null)
         $dom->normalizeDocument();
 
         libxml_use_internal_errors($internalErrors);
-        if (LIBXML_VERSION < 20900) {
+        if (\LIBXML_VERSION < 20900) {
             libxml_disable_entity_loader($disableEntities);
         }
 
         foreach ($dom->childNodes as $child) {
-            if (XML_DOCUMENT_TYPE_NODE === $child->nodeType) {
+            if (\XML_DOCUMENT_TYPE_NODE === $child->nodeType) {
                 throw new XmlParsingException('Document types are not allowed.');
             }
         }
@@ -267,7 +267,7 @@ protected static function getXmlErrors($internalErrors)
         $errors = [];
         foreach (libxml_get_errors() as $error) {
             $errors[] = sprintf('[%s %s] %s (in %s - line %d, column %d)',
-                LIBXML_ERR_WARNING == $error->level ? 'WARNING' : 'ERROR',
+                \LIBXML_ERR_WARNING == $error->level ? 'WARNING' : 'ERROR',
                 $error->code,
                 trim($error->message),
                 $error->file ?: 'n/a',