diff --git a/public_html/includes/class/class.LSformRule_filesize.php b/public_html/includes/class/class.LSformRule_filesize.php
index 89752155..cdcce2cb 100644
--- a/public_html/includes/class/class.LSformRule_filesize.php
+++ b/public_html/includes/class/class.LSformRule_filesize.php
@@ -39,9 +39,10 @@ class LSformRule_filesize extends LSformRule {
    * @return boolean true si la valeur est valide, false sinon
    */
   public static function validate ($value,$options,$formElement) {
-    $file = LSsession :: getTmpFile($value);
-
-    $size = filesize($file);
+    // According to PHP doc, strlen() returns the number of bytes rather
+    // than the number of characters in a string.
+    // See: https://www.php.net/manual/en/function.strlen.php
+    $size = strlen($value);
 
     $maxSize = LSconfig :: get('params.maxSize', null, 'int', $options);
     if (is_int($maxSize) && $size > $maxSize)