diff --git a/src/Symfony/Component/Validator/Constraints/FileValidator.php b/src/Symfony/Component/Validator/Constraints/FileValidator.php
index 52e937944188b..31218c2020fa8 100644
--- a/src/Symfony/Component/Validator/Constraints/FileValidator.php
+++ b/src/Symfony/Component/Validator/Constraints/FileValidator.php
@@ -13,8 +13,10 @@
 
 use Symfony\Component\HttpFoundation\File\File as FileObject;
 use Symfony\Component\HttpFoundation\File\UploadedFile;
+use Symfony\Component\Mime\MimeTypes;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\LogicException;
 use Symfony\Component\Validator\Exception\UnexpectedTypeException;
 use Symfony\Component\Validator\Exception\UnexpectedValueException;
 
@@ -170,12 +172,17 @@ public function validate($value, Constraint $constraint)
         }
 
         if ($constraint->mimeTypes) {
-            if (!$value instanceof FileObject) {
-                $value = new FileObject($value);
+            if ($value instanceof FileObject) {
+                $mime = $value->getMimeType();
+            } elseif (class_exists(MimeTypes::class)) {
+                $mime = MimeTypes::getDefault()->guessMimeType($path);
+            } elseif (!class_exists(FileObject::class)) {
+                throw new LogicException('You cannot validate the mime-type of files as the Mime component is not installed. Try running "composer require symfony/mime".');
+            } else {
+                $mime = (new FileObject($value))->getMimeType();
             }
 
             $mimeTypes = (array) $constraint->mimeTypes;
-            $mime = $value->getMimeType();
 
             foreach ($mimeTypes as $mimeType) {
                 if ($mimeType === $mime) {
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php b/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php
index 0bbac3c6b70a9..c2f45e164a46e 100644
--- a/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php
+++ b/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php
@@ -294,10 +294,10 @@ public function testValidMimeType()
         $file
             ->expects($this->once())
             ->method('getMimeType')
-            ->willReturn('image/jpg');
+            ->willReturn('image/jpeg');
 
         $constraint = new File([
-            'mimeTypes' => ['image/png', 'image/jpg'],
+            'mimeTypes' => ['image/png', 'image/jpeg'],
         ]);
 
         $this->validator->validate($file, $constraint);