diff --git a/.gitattributes b/.gitattributes
index 66ad8a0..28199f2 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -7,3 +7,4 @@
 /.scrutinizer.yml   export-ignore
 /.travis.yml        export-ignore
 /phpunit.xml        export-ignore
+/.php_cs.dist       export-ignore
diff --git a/.php_cs.dist b/.php_cs.dist
new file mode 100644
index 0000000..f7d7a35
--- /dev/null
+++ b/.php_cs.dist
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+return PhpCsFixer\Config::create()
+    ->setUsingCache(false)
+    ->setRules([
+        'native_function_invocation' => [
+            'exclude' => []
+        ],
+    ])
+    ->setRiskyAllowed(true)
+    ->setFinder(
+        PhpCsFixer\Finder::create()
+            ->in(__DIR__ . '/src')
+            ->append([__FILE__])
+    )
+;
diff --git a/.travis.yml b/.travis.yml
index 258b24d..3153955 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -10,6 +10,11 @@ matrix:
       - php vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover
       after_script:
       - php vendor/bin/ocular code-coverage:upload --format=php-clover coverage.clover
+    - php: 7.3
+      script:
+      - composer test-cs
+      - composer test-md
+      - composer test-cs-fixer
 before_script:
 - travis_retry composer self-update
 - travis_retry composer install --no-interaction --prefer-dist
diff --git a/composer.json b/composer.json
index 4b1eec5..dee7b7c 100644
--- a/composer.json
+++ b/composer.json
@@ -32,7 +32,8 @@
     "mockery/mockery": "^1.0",
     "scrutinizer/ocular": "^1.4",
     "squizlabs/php_codesniffer": "^2.9",
-    "phpmd/phpmd": "^2.6"
+    "phpmd/phpmd": "^2.6",
+    "friendsofphp/php-cs-fixer": "^2.14"
   },
   "minimum-stability": "stable",
   "autoload": {
@@ -46,10 +47,12 @@
     }
   },
   "scripts": {
-    "test": ["@test-unit", "@test-cs", "@test-md"],
+    "test": ["@test-unit", "@test-cs", "@test-md", "@test-cs-fixer"],
     "test-unit": "./vendor/phpunit/phpunit/phpunit --coverage-text",
     "test-unit-phpdbg": "phpdbg -qrr ./vendor/bin/phpunit --coverage-text",
     "test-cs": "./vendor/bin/phpcs -p -s --standard=PSR2 ./src ./tests",
-    "test-md": "./vendor/bin/phpmd ./src text codesize,controversial,cleancode,design,unusedcode,naming"
+    "test-md": "./vendor/bin/phpmd ./src text codesize,controversial,cleancode,design,unusedcode,naming",
+    "test-cs-fixer": "./vendor/bin/php-cs-fixer fix --diff --dry-run -v",
+    "cs-fixer": "./vendor/bin/php-cs-fixer fix --diff -v --ansi"
   }
 }
diff --git a/src/Analyzer.php b/src/Analyzer.php
index 04e2c45..73a303b 100644
--- a/src/Analyzer.php
+++ b/src/Analyzer.php
@@ -213,7 +213,7 @@ protected function analyzeAsPreFlight(RequestInterface $request, string $request
 
             return $this->createResult(AnalysisResultInterface::TYPE_REQUEST_OUT_OF_CORS_SCOPE);
         }
-        $requestMethod = reset($requestMethod);
+        $requestMethod = \reset($requestMethod);
 
         // OK now we are sure it's a pre-flight request
         $this->logDebug('Request is identified as a pre-flight CORS request.');
@@ -280,7 +280,7 @@ protected function createPreFlightResponseHeaders(
 
         // #6.2.10
         // Has only 'simple' headers excluding Content-Type
-        $isSimpleExclCT = empty(array_diff($lcRequestHeaders, static::SIMPLE_LC_HEADERS_EXCLUDING_CONTENT_TYPE));
+        $isSimpleExclCT = empty(\array_diff($lcRequestHeaders, static::SIMPLE_LC_HEADERS_EXCLUDING_CONTENT_TYPE));
         if ($isSimpleExclCT === false || $this->strategy->isForceAddAllowedHeadersToPreFlightResponse() === true) {
             $headers[CorsResponseHeaders::ALLOW_HEADERS] = $this->strategy->getRequestAllowedHeaders($request);
         }
@@ -298,10 +298,10 @@ protected function getRequestedHeadersInLowerCase(RequestInterface $request): ar
         $requestHeaders = [];
 
         foreach ($request->getHeader(CorsRequestHeaders::HEADERS) as $headersList) {
-            $headersList = strtolower($headersList);
-            foreach (explode(CorsRequestHeaders::HEADERS_SEPARATOR, $headersList) as $header) {
+            $headersList = \strtolower($headersList);
+            foreach (\explode(CorsRequestHeaders::HEADERS_SEPARATOR, $headersList) as $header) {
                 // after explode header names might have spaces in the beginnings and ends so trim them
-                $header = trim($header);
+                $header = \trim($header);
                 if (empty($header) === false) {
                     $requestHeaders[] = $header;
                 }
@@ -321,7 +321,7 @@ protected function getOriginHeader(RequestInterface $request): string
         if ($request->hasHeader(CorsRequestHeaders::ORIGIN) === true) {
             $header = $request->getHeader(CorsRequestHeaders::ORIGIN);
             if (empty($header) === false) {
-                return reset($header);
+                return \reset($header);
             }
         }
 
@@ -348,15 +348,15 @@ protected function checkIsSameHost(RequestInterface $request): bool
         //
         // `parse_url` function thinks the first value is `path` and the second is `host` with `port`
         // which is a bit annoying so...
-        $portOrNull = parse_url($host, PHP_URL_PORT);
-        $hostUrl    = $portOrNull === null ? $host : parse_url($host, PHP_URL_HOST);
+        $portOrNull = \parse_url($host, PHP_URL_PORT);
+        $hostUrl    = $portOrNull === null ? $host : \parse_url($host, PHP_URL_HOST);
 
         // Neither MDN, nor RFC tell anything definitive about Host header comparison.
         // Browsers such as Firefox and Chrome do not add the optional port for
         // HTTP (80) and HTTPS (443).
         // So we require port match only if it specified in settings.
 
-        $isHostUrlMatch = strcasecmp($serverOriginHost, $hostUrl) === 0;
+        $isHostUrlMatch = \strcasecmp($serverOriginHost, $hostUrl) === 0;
         $isSameHost     =
             $isHostUrlMatch === true &&
             ($serverOriginPort === null || $serverOriginPort === $portOrNull);
@@ -381,7 +381,7 @@ protected function checkIsSameHost(RequestInterface $request): bool
      */
     protected function checkIsCrossOrigin(string $requestOrigin): bool
     {
-        $parsedUrl = parse_url($requestOrigin);
+        $parsedUrl = \parse_url($requestOrigin);
         if ($parsedUrl === false) {
             $this->logWarning('Request origin header URL cannot be parsed.', ['url' => $requestOrigin]);
 
@@ -391,12 +391,12 @@ protected function checkIsCrossOrigin(string $requestOrigin): bool
         // check `host` parts
         $requestOriginHost = $parsedUrl['host'] ?? '';
         $serverOriginHost  = $this->strategy->getServerOriginHost();
-        if (strcasecmp($requestOriginHost, $serverOriginHost) !== 0) {
+        if (\strcasecmp($requestOriginHost, $serverOriginHost) !== 0) {
             return true;
         }
 
         // check `port` parts
-        $requestOriginPort = array_key_exists('port', $parsedUrl) === true ? (int)$parsedUrl['port'] : null;
+        $requestOriginPort = \array_key_exists('port', $parsedUrl) === true ? (int)$parsedUrl['port'] : null;
         $serverOriginPort  = $this->strategy->getServerOriginPort();
         if ($requestOriginPort !== $serverOriginPort) {
             return true;
@@ -405,7 +405,7 @@ protected function checkIsCrossOrigin(string $requestOrigin): bool
         // check `scheme` parts
         $requestOriginScheme = $parsedUrl['scheme'] ?? '';
         $serverOriginScheme  = $this->strategy->getServerOriginScheme();
-        if (strcasecmp($requestOriginScheme, $serverOriginScheme) !== 0) {
+        if (\strcasecmp($requestOriginScheme, $serverOriginScheme) !== 0) {
             return true;
         }
 
@@ -450,7 +450,7 @@ protected static function getFactory(): FactoryInterface
     private function getRequestHostHeader(RequestInterface $request): ?string
     {
         $hostHeaderValue = $request->getHeader(CorsRequestHeaders::HOST);
-        $host            = empty($hostHeaderValue) === true ? null : reset($hostHeaderValue);
+        $host            = empty($hostHeaderValue) === true ? null : \reset($hostHeaderValue);
 
         return $host;
     }
diff --git a/src/Strategies/Settings.php b/src/Strategies/Settings.php
index 935cd84..8d1dcb6 100644
--- a/src/Strategies/Settings.php
+++ b/src/Strategies/Settings.php
@@ -263,16 +263,16 @@ public function getServerOriginPort(): ?int
      */
     public function setServerOrigin(string $scheme, string $host, int $port): self
     {
-        assert(empty($scheme) === false);
-        assert(empty($host) === false);
-        assert(0 < $port && $port <= 0xFFFF);
+        \assert(empty($scheme) === false);
+        \assert(empty($host) === false);
+        \assert(0 < $port && $port <= 0xFFFF);
 
         $this->serverOriginScheme = $scheme;
         $this->serverOriginHost   = $host;
 
-        if (strcasecmp($scheme, 'http') === 0 && $port === 80) {
+        if (\strcasecmp($scheme, 'http') === 0 && $port === 80) {
             $port = null;
-        } elseif (strcasecmp($scheme, 'https') === 0 && $port === 443) {
+        } elseif (\strcasecmp($scheme, 'https') === 0 && $port === 443) {
             $port = null;
         }
         $this->serverOriginPort = $port;
@@ -305,7 +305,7 @@ public function getPreFlightCacheMaxAge(RequestInterface $request): int
      */
     public function setPreFlightCacheMaxAge(int $cacheMaxAge): self
     {
-        assert($cacheMaxAge >= 0);
+        \assert($cacheMaxAge >= 0);
 
         $this->preFlightCacheMaxAge   = $cacheMaxAge;
         $this->isPreFlightCanBeCached = $cacheMaxAge > 0;
@@ -428,7 +428,7 @@ public function isRequestOriginAllowed(string $requestOrigin): bool
     {
         return
             $this->areAllOriginsAllowed === true ||
-            isset($this->allowedOrigins[strtolower($requestOrigin)]) === true;
+            isset($this->allowedOrigins[\strtolower($requestOrigin)]) === true;
     }
 
     /**
@@ -455,7 +455,7 @@ public function setAllowedOrigins(array $origins): self
         $this->allowedOrigins = [];
 
         foreach ($origins as $origin) {
-            $this->allowedOrigins[strtolower($origin)] = true;
+            $this->allowedOrigins[\strtolower($origin)] = true;
         }
 
         $this->areAllOriginsAllowed = false;
@@ -468,7 +468,7 @@ public function setAllowedOrigins(array $origins): self
      */
     public function isRequestMethodSupported(string $method): bool
     {
-        return $this->areAllMethodsAllowed === true || isset($this->allowedLcMethods[strtolower($method)]) === true;
+        return $this->areAllMethodsAllowed === true || isset($this->allowedLcMethods[\strtolower($method)]) === true;
     }
 
     /**
@@ -500,11 +500,11 @@ public function enableAllMethodsAllowed(): self
      */
     public function setAllowedMethods(array $methods): self
     {
-        $this->allowedMethodsList = implode(', ', $methods);
+        $this->allowedMethodsList = \implode(', ', $methods);
 
         $this->allowedLcMethods = [];
         foreach ($methods as $method) {
-            $this->allowedLcMethods[strtolower($method)] = true;
+            $this->allowedLcMethods[\strtolower($method)] = true;
         }
 
         $this->areAllMethodsAllowed = false;
@@ -518,7 +518,7 @@ public function setAllowedMethods(array $methods): self
     public function isRequestAllHeadersSupported(array $lcHeaders): bool
     {
         return $this->areAllHeadersAllowed === true ||
-            count(array_intersect($this->allowedLcHeaders, $lcHeaders)) === count($lcHeaders);
+            \count(\array_intersect($this->allowedLcHeaders, $lcHeaders)) === \count($lcHeaders);
     }
 
     /**
@@ -550,11 +550,11 @@ public function enableAllHeadersAllowed(): self
      */
     public function setAllowedHeaders(array $headers): self
     {
-        $this->allowedHeadersList = implode(', ', $headers);
+        $this->allowedHeadersList = \implode(', ', $headers);
 
         $this->allowedLcHeaders = [];
         foreach ($headers as $header) {
-            $this->allowedLcHeaders[] = strtolower($header);
+            $this->allowedLcHeaders[] = \strtolower($header);
         }
 
         $this->areAllHeadersAllowed = false;
@@ -599,12 +599,12 @@ public function setExposedHeaders(array $headers): self
         // make sense to include those headers to exposed.
         $filtered = [];
         foreach ($headers as $header) {
-            if (in_array(strtolower($header), static::SIMPLE_LC_RESPONSE_HEADERS) === false) {
+            if (\in_array(\strtolower($header), static::SIMPLE_LC_RESPONSE_HEADERS) === false) {
                 $filtered[] = $header;
             }
         }
 
-        $this->exposedHeadersList = implode(', ', $filtered);
+        $this->exposedHeadersList = \implode(', ', $filtered);
 
         return $this;
     }