diff --git a/admin/classes/local/settings/filesize.php b/admin/classes/local/settings/filesize.php
index 3352f1ec375..4af33f5b67a 100644
--- a/admin/classes/local/settings/filesize.php
+++ b/admin/classes/local/settings/filesize.php
@@ -126,6 +126,7 @@ class filesize extends \admin_setting {
         if (is_null($bytes)) {
             return null;
         }
+        $bytes = intval($bytes);
 
         return self::parse_bytes($bytes);
     }
@@ -145,9 +146,10 @@ class filesize extends \admin_setting {
             return get_string('errorsetting', 'admin');
         }
 
+        // Calculate size in bytes, ensuring we don't overflow PHP_INT_MAX.
         $bytes = $data['v'] * $data['u'];
+        $result = (is_int($bytes) && $this->config_write($this->name, $bytes));
 
-        $result = $this->config_write($this->name, $bytes);
         return ($result ? '' : get_string('errorsetting', 'admin'));
     }