diff --git a/src/Symfony/Component/Validator/Constraints/LengthValidator.php b/src/Symfony/Component/Validator/Constraints/LengthValidator.php
index 01955ed03571..0c11dfca8466 100644
--- a/src/Symfony/Component/Validator/Constraints/LengthValidator.php
+++ b/src/Symfony/Component/Validator/Constraints/LengthValidator.php
@@ -39,8 +39,14 @@ public function validate($value, Constraint $constraint)
 
         $stringValue = (string) $value;
 
-        if (!$invalidCharset = !@mb_check_encoding($stringValue, $constraint->charset)) {
-            $length = mb_strlen($stringValue, $constraint->charset);
+        try {
+            $invalidCharset = !@mb_check_encoding($stringValue, $constraint->charset);
+        } catch (\ValueError $e) {
+            if (!str_starts_with($e->getMessage(), 'mb_check_encoding(): Argument #2 ($encoding) must be a valid encoding')) {
+                throw $e;
+            }
+
+            $invalidCharset = true;
         }
 
         if ($invalidCharset) {
@@ -54,6 +60,8 @@ public function validate($value, Constraint $constraint)
             return;
         }
 
+        $length = mb_strlen($stringValue, $constraint->charset);
+
         if (null !== $constraint->max && $length > $constraint->max) {
             $this->context->buildViolation($constraint->min == $constraint->max ? $constraint->exactMessage : $constraint->maxMessage)
                 ->setParameter('{{ value }}', $this->formatValue($stringValue))