diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0cc1d801..8e93f1b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add support for Symfony 7
 - Remove support of PHP 7.4
 
+### Fixed
+
+- Prevent letters as number
+
 ## [3.9.3] - 2023-11-29
 
 ### Added
diff --git a/src/Form/DataTransformer/PhoneNumberToArrayTransformer.php b/src/Form/DataTransformer/PhoneNumberToArrayTransformer.php
index 32f284e7..6c73586c 100644
--- a/src/Form/DataTransformer/PhoneNumberToArrayTransformer.php
+++ b/src/Form/DataTransformer/PhoneNumberToArrayTransformer.php
@@ -74,6 +74,10 @@ public function reverseTransform($value): ?PhoneNumber
 
         $util = PhoneNumberUtil::getInstance();
 
+        if (preg_match('/\p{L}/u', $value['number'])) {
+            throw new TransformationFailedException('The number can not contain letters.');
+        }
+
         try {
             $phoneNumber = $util->parse($value['number'], $value['country']);
         } catch (NumberParseException $e) {
diff --git a/src/Form/DataTransformer/PhoneNumberToStringTransformer.php b/src/Form/DataTransformer/PhoneNumberToStringTransformer.php
index c203b5dc..44fbc09e 100644
--- a/src/Form/DataTransformer/PhoneNumberToStringTransformer.php
+++ b/src/Form/DataTransformer/PhoneNumberToStringTransformer.php
@@ -76,6 +76,10 @@ public function reverseTransform($value): ?PhoneNumber
             return null;
         }
 
+        if (preg_match('/\p{L}/u', $value)) {
+            throw new TransformationFailedException('The number can not contain letters.');
+        }
+
         try {
             return PhoneNumberUtil::getInstance()->parse($value, $this->defaultRegion);
         } catch (NumberParseException $e) {