diff --git a/packages/CodingStandard/src/Fixer/Php/ClassStringToClassConstantFixer.php b/packages/CodingStandard/src/Fixer/Php/ClassStringToClassConstantFixer.php
new file mode 100644
index 00000000000..08b1681d7ac
--- /dev/null
+++ b/packages/CodingStandard/src/Fixer/Php/ClassStringToClassConstantFixer.php
@@ -0,0 +1,88 @@
+<?php declare(strict_types=1);
+
+namespace Symplify\CodingStandard\Fixer\Php;
+
+use Nette\Utils\Strings;
+use PhpCsFixer\Fixer\DefinedFixerInterface;
+use PhpCsFixer\FixerDefinition\CodeSample;
+use PhpCsFixer\FixerDefinition\FixerDefinition;
+use PhpCsFixer\FixerDefinition\FixerDefinitionInterface;
+use PhpCsFixer\Tokenizer\CT;
+use PhpCsFixer\Tokenizer\Token;
+use PhpCsFixer\Tokenizer\Tokens;
+use SplFileInfo;
+
+final class ClassStringToClassConstantFixer implements DefinedFixerInterface
+{
+    public function getDefinition(): FixerDefinitionInterface
+    {
+        return new FixerDefinition(
+            '::class refences should be used over string.',
+            [
+                new CodeSample(
+'<?php      
+
+$className = "DateTime";  
+                '),
+                new CodeSample(
+'<?php      
+
+$interfaceName = "DateTimeInterface";  
+                '),
+            ]
+        );
+    }
+
+    public function isCandidate(Tokens $tokens): bool
+    {
+        return true;
+    }
+
+    public function fix(SplFileInfo $file, Tokens $tokens): void
+    {
+        foreach (array_reverse($tokens->toArray(), true) as $index => $token) {
+            /** @var Token $token */
+            if (! $this->isStringToken($token)) {
+                continue;
+            }
+
+            $potentialClassOrInterfaceName = trim($token->getContent(), "'");
+            if (class_exists($potentialClassOrInterfaceName) || interface_exists($potentialClassOrInterfaceName)) {
+                $token->clear(); // overrideAt() fails on "Illegal offset type"
+                $tokens->insertAt($index, [
+                    new Token([T_NS_SEPARATOR, '\\']),
+                    new Token([T_STRING, $potentialClassOrInterfaceName]),
+                    new Token([T_DOUBLE_COLON, '::']),
+                    new Token([CT::T_CLASS_CONSTANT, 'class']),
+                ]);
+            }
+        }
+    }
+
+    public function isRisky(): bool
+    {
+        return false;
+    }
+
+    public function getName(): string
+    {
+        return self::class;
+    }
+
+    public function getPriority(): int
+    {
+        // @todo combine with namespace import fixer/sniff
+        return 0;
+    }
+
+    public function supports(SplFileInfo $file): bool
+    {
+        return true;
+    }
+
+    private function isStringToken(Token $token): bool
+    {
+        return Strings::startsWith($token->getContent(), "'")
+            && Strings::endsWith($token->getContent(), "'");
+    }
+}
diff --git a/packages/CodingStandard/tests/Fixer/Php/ClassStringToClassConstantFixerTest.php b/packages/CodingStandard/tests/Fixer/Php/ClassStringToClassConstantFixerTest.php
new file mode 100644
index 00000000000..567286422aa
--- /dev/null
+++ b/packages/CodingStandard/tests/Fixer/Php/ClassStringToClassConstantFixerTest.php
@@ -0,0 +1,40 @@
+<?php declare(strict_types=1);
+
+namespace Symplify\CodingStandard\Tests\Fixer\Php;
+
+use PhpCsFixer\Fixer\FixerInterface;
+use PhpCsFixer\Test\AbstractFixerTestCase;
+use Symplify\CodingStandard\Fixer\Php\ClassStringToClassConstantFixer;
+
+final class ClassStringToClassConstantFixerTest extends AbstractFixerTestCase
+{
+    /**
+     * @dataProvider provideFixCases()
+     */
+    public function testFix(string $expected, string $input): void
+    {
+        $this->doTest($expected, $input);
+    }
+
+    /**
+     * @return string[][]
+     */
+    public function provideFixCases(): array
+    {
+        return [
+            [
+                file_get_contents(__DIR__ . '/fixed/fixed.php.inc'),
+                file_get_contents(__DIR__ . '/wrong/wrong.php.inc'),
+            ],
+            [
+                file_get_contents(__DIR__ . '/fixed/fixed2.php.inc'),
+                file_get_contents(__DIR__ . '/wrong/wrong2.php.inc'),
+            ],
+        ];
+    }
+
+    protected function createFixer(): FixerInterface
+    {
+        return new ClassStringToClassConstantFixer;
+    }
+}
diff --git a/packages/CodingStandard/tests/Fixer/Php/fixed/fixed.php.inc b/packages/CodingStandard/tests/Fixer/Php/fixed/fixed.php.inc
new file mode 100644
index 00000000000..316e0f7feb0
--- /dev/null
+++ b/packages/CodingStandard/tests/Fixer/Php/fixed/fixed.php.inc
@@ -0,0 +1,3 @@
+<?php
+
+$classType = \DateTime::class;
\ No newline at end of file
diff --git a/packages/CodingStandard/tests/Fixer/Php/fixed/fixed2.php.inc b/packages/CodingStandard/tests/Fixer/Php/fixed/fixed2.php.inc
new file mode 100644
index 00000000000..d150c8a687e
--- /dev/null
+++ b/packages/CodingStandard/tests/Fixer/Php/fixed/fixed2.php.inc
@@ -0,0 +1,3 @@
+<?php
+
+$classType = \DateTimeInterface::class;
\ No newline at end of file
diff --git a/packages/CodingStandard/tests/Fixer/Php/wrong/wrong.php.inc b/packages/CodingStandard/tests/Fixer/Php/wrong/wrong.php.inc
new file mode 100644
index 00000000000..e52528e7843
--- /dev/null
+++ b/packages/CodingStandard/tests/Fixer/Php/wrong/wrong.php.inc
@@ -0,0 +1,3 @@
+<?php
+
+$classType = 'DateTime';
\ No newline at end of file
diff --git a/packages/CodingStandard/tests/Fixer/Php/wrong/wrong2.php.inc b/packages/CodingStandard/tests/Fixer/Php/wrong/wrong2.php.inc
new file mode 100644
index 00000000000..638e93de2c5
--- /dev/null
+++ b/packages/CodingStandard/tests/Fixer/Php/wrong/wrong2.php.inc
@@ -0,0 +1,3 @@
+<?php
+
+$classType = 'DateTimeInterface';
\ No newline at end of file