diff --git a/src/Symfony/Component/Validator/Constraints/FileValidator.php b/src/Symfony/Component/Validator/Constraints/FileValidator.php
index e4e02c80fd18b..363183ec4d4bb 100644
--- a/src/Symfony/Component/Validator/Constraints/FileValidator.php
+++ b/src/Symfony/Component/Validator/Constraints/FileValidator.php
@@ -171,7 +171,7 @@ public function validate(mixed $value, Constraint $constraint)
         $mimeTypes = (array) $constraint->mimeTypes;
 
         if ($constraint->extensions) {
-            $fileExtension = pathinfo($basename, \PATHINFO_EXTENSION);
+            $fileExtension = strtolower(pathinfo($basename, \PATHINFO_EXTENSION));
 
             $found = false;
             $normalizedExtensions = [];
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php b/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php
index bb2b19eef204e..3643adee821a3 100644
--- a/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php
+++ b/src/Symfony/Component/Validator/Tests/Constraints/FileValidatorTest.php
@@ -556,6 +556,7 @@ private function validExtensionProvider(): iterable
         yield ['test.gif'];
         yield ['test.png.gif'];
         yield ['ccc.txt'];
+        yield ['uppercased-extension.TXT'];
     }
 
     /**
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/Fixtures/uppercased-extension.TXT b/src/Symfony/Component/Validator/Tests/Constraints/Fixtures/uppercased-extension.TXT
new file mode 100644
index 0000000000000..323fae03f4606
--- /dev/null
+++ b/src/Symfony/Component/Validator/Tests/Constraints/Fixtures/uppercased-extension.TXT
@@ -0,0 +1 @@
+foobar