diff --git a/README.rst b/README.rst
index 6accd80ef8d..f9894b29e12 100644
--- a/README.rst
+++ b/README.rst
@@ -431,6 +431,10 @@ Choose from the list of available rules:
 
   *Risky rule: forcing strict types will stop non strict code from working.*
 
+* **declared_class_casing** [@Symfony, @PhpCsFixer]
+
+  Classes should be referred to using the correct casing.
+
 * **dir_constant** [@Symfony:risky, @PhpCsFixer:risky]
 
   Replaces ``dirname(__FILE__)`` expression with equivalent ``__DIR__``
diff --git a/src/Fixer/Casing/DeclaredClassCasingFixer.php b/src/Fixer/Casing/DeclaredClassCasingFixer.php
new file mode 100644
index 00000000000..0714b6d118b
--- /dev/null
+++ b/src/Fixer/Casing/DeclaredClassCasingFixer.php
@@ -0,0 +1,116 @@
+<?php
+
+/*
+ * This file is part of PHP CS Fixer.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *     Dariusz Rumiński <dariusz.ruminski@gmail.com>
+ *
+ * This source file is subject to the MIT license that is bundled
+ * with this source code in the file LICENSE.
+ */
+
+namespace PhpCsFixer\Fixer\Casing;
+
+use PhpCsFixer\AbstractFixer;
+use PhpCsFixer\FixerDefinition\CodeSample;
+use PhpCsFixer\FixerDefinition\FixerDefinition;
+use PhpCsFixer\Tokenizer\CT;
+use PhpCsFixer\Tokenizer\Token;
+use PhpCsFixer\Tokenizer\Tokens;
+
+/**
+ * @author siad007
+ */
+final class DeclaredClassCasingFixer extends AbstractFixer
+{
+    /**
+     * @var string[]
+     */
+    private static $declaredClassNames;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getDefinition()
+    {
+        return new FixerDefinition(
+            'Classes should be referred to using the correct casing.',
+            [new CodeSample("<?php\nnew STDCLASS();\n")]
+        );
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isCandidate(Tokens $tokens)
+    {
+        return $tokens->isTokenKindFound(T_STRING);
+    }
+
+    /**
+     * @param \SplFileInfo $file
+     * @param Tokens       $tokens
+     */
+    protected function applyFix(\SplFileInfo $file, Tokens $tokens)
+    {
+        if (null === self::$declaredClassNames) {
+            foreach (get_declared_classes() as $class) {
+                self::$declaredClassNames[strtolower($class)] = $class;
+            }
+        }
+
+        foreach ($tokens as $index => $token) {
+            $name = $this->declaredClass($index, $token, $tokens);
+
+            if (null !== $name) {
+                $tokens[$index] = new Token([T_STRING, self::$declaredClassNames[$name]]);
+            }
+        }
+    }
+
+    /**
+     * Get the lower case name of the declared class or null.
+     *
+     * @param int    $index
+     * @param Token  $token
+     * @param Tokens $tokens
+     *
+     * @return null|string
+     */
+    private function declaredClass($index, Token $token, Tokens $tokens)
+    {
+        $lower = strtolower($token->getContent());
+
+        if (!\array_key_exists($lower, self::$declaredClassNames)) {
+            return null;
+        }
+
+        $notBeforeTypes = [
+            T_CLASS,
+            T_AS,
+            T_DOUBLE_COLON,
+            T_OBJECT_OPERATOR,
+            T_FUNCTION,
+            T_CONST,
+            T_TRAIT,
+            T_USE,
+            CT::T_USE_TRAIT,
+        ];
+
+        $beforeClassName = $tokens->getPrevMeaningfulToken($index);
+
+        if ($tokens[$beforeClassName]->isGivenKind($notBeforeTypes)) {
+            return null;
+        }
+
+        if (
+            $tokens[$beforeClassName]->isGivenKind(T_NS_SEPARATOR)
+            && $tokens[$tokens->getPrevMeaningfulToken($beforeClassName)]->isGivenKind([T_STRING])
+        ) {
+            return null;
+        }
+
+        return $lower;
+    }
+}
diff --git a/src/RuleSet.php b/src/RuleSet.php
index 26b2100e2ea..ac44a80df00 100644
--- a/src/RuleSet.php
+++ b/src/RuleSet.php
@@ -70,6 +70,7 @@ final class RuleSet implements RuleSetInterface
             'class_definition' => ['single_line' => true],
             'concat_space' => ['spacing' => 'none'],
             'declare_equal_normalize' => true,
+            'declared_class_casing' => true,
             'function_typehint_space' => true,
             'include' => true,
             'increment_style' => true,
diff --git a/tests/Fixer/Casing/DeclaredClassCasingFixerTest.php b/tests/Fixer/Casing/DeclaredClassCasingFixerTest.php
new file mode 100644
index 00000000000..8a59785c422
--- /dev/null
+++ b/tests/Fixer/Casing/DeclaredClassCasingFixerTest.php
@@ -0,0 +1,139 @@
+<?php
+
+/*
+ * This file is part of PHP CS Fixer.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *     Dariusz Rumiński <dariusz.ruminski@gmail.com>
+ *
+ * This source file is subject to the MIT license that is bundled
+ * with this source code in the file LICENSE.
+ */
+
+namespace PhpCsFixer\Tests\Fixer\Casing;
+
+use PhpCsFixer\Console\Application;
+use PhpCsFixer\Tests\Test\AbstractFixerTestCase;
+
+/**
+ * @author siad007
+ *
+ * @internal
+ *
+ * @covers \PhpCsFixer\Fixer\Casing\DeclaredClassCasingFixer
+ */
+final class DeclaredClassCasingFixerTest extends AbstractFixerTestCase
+{
+    /**
+     * @param string      $expected
+     * @param null|string $input
+     *
+     * @dataProvider provideFixCases
+     */
+    public function testFix($expected, $input = null)
+    {
+        $this->doTest($expected, $input);
+    }
+
+    public function provideFixCases()
+    {
+        return [
+            [
+                '<?php
+                    $stdclass = new \stdClass();
+                    $stdclass = new stdClass();
+                ',
+                '<?php
+                    $stdclass = new \STDCLASS();
+                    $stdclass = new STDCLASS();
+                ',
+            ],
+            [
+                '<?php
+
+                namespace Foo;
+
+                class exception extends \Exception
+                {
+                }
+                ',
+                '<?php
+
+                namespace Foo;
+
+                class exception extends \EXCEPTION
+                {
+                }
+                ',
+            ],
+            [
+                '<?php
+
+                echo \Exception::class;
+                echo Exception::class;
+                ',
+                '<?php
+
+                echo \ExCePTion::class;
+                echo ExCePTion::class;
+                ',
+            ],
+            [
+                '<?php
+
+                $a::exception();
+                ',
+            ],
+            [
+                '<?php
+
+                $a->exception();
+                ',
+            ],
+            [
+                '<?php
+
+                function exception() {};
+                ',
+            ],
+            [
+                '<?php
+
+                echo "This is an " . "exception";
+                ',
+            ],
+            [
+                '<?php
+
+                namespace Foo;
+
+                trait stdclass
+                {
+                }
+
+                use Foo\stdclass as exception;
+
+                class test
+                {
+                    use exception;
+                }
+                ',
+            ],
+            [
+                '<?php
+                use stdClass as exception;
+                ',
+            ],
+            [
+                '<?php
+                class Foo {
+                    const stdclass = 1;
+                }
+                ',
+            ],
+            'imported constant '.Application::VERSION => [
+                sprintf('<?php echo %s::VERSION; new PhpCsFixer\Console\APPLICATION();', strtoupper(Application::class)),
+            ],
+        ];
+    }
+}