diff --git a/Crypto/SMimeEncrypter.php b/Crypto/SMimeEncrypter.php
index d6961a6..9081860 100644
--- a/Crypto/SMimeEncrypter.php
+++ b/Crypto/SMimeEncrypter.php
@@ -38,7 +38,7 @@ public function __construct($certificate, int $cipher = null)
             $this->certs = $this->normalizeFilePath($certificate);
         }
 
-        $this->cipher = $cipher ?? OPENSSL_CIPHER_AES_256_CBC;
+        $this->cipher = $cipher ?? \OPENSSL_CIPHER_AES_256_CBC;
     }
 
     public function encrypt(Message $message): Message
diff --git a/Crypto/SMimeSigner.php b/Crypto/SMimeSigner.php
index 1b55537..5b94a45 100644
--- a/Crypto/SMimeSigner.php
+++ b/Crypto/SMimeSigner.php
@@ -45,7 +45,7 @@ public function __construct(string $certificate, string $privateKey, string $pri
             $this->signPrivateKey = $this->normalizeFilePath($privateKey);
         }
 
-        $this->signOptions = $signOptions ?? PKCS7_DETACHED;
+        $this->signOptions = $signOptions ?? \PKCS7_DETACHED;
         $this->extraCerts = $extraCerts ? realpath($extraCerts) : null;
     }
 
diff --git a/Encoder/Base64ContentEncoder.php b/Encoder/Base64ContentEncoder.php
index cb7f911..338490b 100644
--- a/Encoder/Base64ContentEncoder.php
+++ b/Encoder/Base64ContentEncoder.php
@@ -24,7 +24,7 @@ public function encodeByteStream($stream, int $maxLineLength = 0): iterable
             throw new \TypeError(sprintf('Method "%s" takes a stream as a first argument.', __METHOD__));
         }
 
-        $filter = stream_filter_append($stream, 'convert.base64-encode', STREAM_FILTER_READ, [
+        $filter = stream_filter_append($stream, 'convert.base64-encode', \STREAM_FILTER_READ, [
             'line-length' => 0 >= $maxLineLength || 76 < $maxLineLength ? 76 : $maxLineLength,
             'line-break-chars' => "\r\n",
         ]);
diff --git a/Encoder/IdnAddressEncoder.php b/Encoder/IdnAddressEncoder.php
index cdd5d4c..69ab887 100644
--- a/Encoder/IdnAddressEncoder.php
+++ b/Encoder/IdnAddressEncoder.php
@@ -43,7 +43,7 @@ public function encodeString(string $address): string
             }
 
             if (preg_match('/[^\x00-\x7F]/', $domain)) {
-                $address = sprintf('%s@%s', $local, idn_to_ascii($domain, 0, INTL_IDNA_VARIANT_UTS46));
+                $address = sprintf('%s@%s', $local, idn_to_ascii($domain, 0, \INTL_IDNA_VARIANT_UTS46));
             }
         }
 
diff --git a/FileinfoMimeTypeGuesser.php b/FileinfoMimeTypeGuesser.php
index 3028159..c6c7559 100644
--- a/FileinfoMimeTypeGuesser.php
+++ b/FileinfoMimeTypeGuesser.php
@@ -54,7 +54,7 @@ public function guessMimeType(string $path): ?string
             throw new LogicException(sprintf('The "%s" guesser is not supported.', __CLASS__));
         }
 
-        if (false === $finfo = new \finfo(FILEINFO_MIME_TYPE, $this->magicFile)) {
+        if (false === $finfo = new \finfo(\FILEINFO_MIME_TYPE, $this->magicFile)) {
             return null;
         }
         $mimeType = $finfo->file($path);
diff --git a/Header/AbstractHeader.php b/Header/AbstractHeader.php
index 548c192..e93b87a 100644
--- a/Header/AbstractHeader.php
+++ b/Header/AbstractHeader.php
@@ -220,7 +220,7 @@ protected function getTokenAsEncodedWord(string $token, int $firstLineOffset = 0
      */
     protected function generateTokenLines(string $token): array
     {
-        return preg_split('~(\r\n)~', $token, -1, PREG_SPLIT_DELIM_CAPTURE);
+        return preg_split('~(\r\n)~', $token, -1, \PREG_SPLIT_DELIM_CAPTURE);
     }
 
     /**
diff --git a/Part/Multipart/FormDataPart.php b/Part/Multipart/FormDataPart.php
index 6838620..c293efe 100644
--- a/Part/Multipart/FormDataPart.php
+++ b/Part/Multipart/FormDataPart.php
@@ -40,7 +40,7 @@ public function __construct(array $fields = [])
             $this->fields[$name] = $value;
         }
         // HTTP does not support \r\n in header values
-        $this->getHeaders()->setMaxLineLength(PHP_INT_MAX);
+        $this->getHeaders()->setMaxLineLength(\PHP_INT_MAX);
     }
 
     public function getMediaSubtype(): string
@@ -95,7 +95,7 @@ private function configurePart(string $name, TextPart $part): TextPart
         $part->setDisposition('form-data');
         $part->setName($name);
         // HTTP does not support \r\n in header values
-        $part->getHeaders()->setMaxLineLength(PHP_INT_MAX);
+        $part->getHeaders()->setMaxLineLength(\PHP_INT_MAX);
         $r->setValue($part, '8bit');
 
         return $part;
diff --git a/Tests/Crypto/SMimeSignerTest.php b/Tests/Crypto/SMimeSignerTest.php
index 5522bc6..ed13d04 100644
--- a/Tests/Crypto/SMimeSignerTest.php
+++ b/Tests/Crypto/SMimeSignerTest.php
@@ -143,7 +143,7 @@ public function testSignedMessageExtraCerts()
             $this->samplesDir.'sign.key',
             null,
             $this->samplesDir.'intermediate.crt',
-            PKCS7_DETACHED
+            \PKCS7_DETACHED
         );
         $signedMessage = $signer->sign($message);
 
diff --git a/Tests/Part/Multipart/FormDataPartTest.php b/Tests/Part/Multipart/FormDataPartTest.php
index 6f81224..417417f 100644
--- a/Tests/Part/Multipart/FormDataPartTest.php
+++ b/Tests/Part/Multipart/FormDataPartTest.php
@@ -35,14 +35,14 @@ public function testConstructor()
         $t = new TextPart($content, 'utf-8', 'plain', '8bit');
         $t->setDisposition('form-data');
         $t->setName('foo');
-        $t->getHeaders()->setMaxLineLength(PHP_INT_MAX);
+        $t->getHeaders()->setMaxLineLength(\PHP_INT_MAX);
         $b->setDisposition('form-data');
         $b->setName('bar');
-        $b->getHeaders()->setMaxLineLength(PHP_INT_MAX);
+        $b->getHeaders()->setMaxLineLength(\PHP_INT_MAX);
         $r->setValue($b, '8bit');
         $c->setDisposition('form-data');
         $c->setName('baz');
-        $c->getHeaders()->setMaxLineLength(PHP_INT_MAX);
+        $c->getHeaders()->setMaxLineLength(\PHP_INT_MAX);
         $r->setValue($c, '8bit');
         $this->assertEquals([$t, $b, $c], $f->getParts());
     }