diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8d7ef819..8a924ca3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed PHP8.1 deprecation notices for strftime [#672](https://github.com/smarty-php/smarty/issues/672)
 - Fixed PHP8.1 deprecation errors passing null to parameter in trim [#807](https://github.com/smarty-php/smarty/pull/807)
 - Adapt Smarty upper/lower functions to be codesafe (e.g. for Turkish locale) [#586](https://github.com/smarty-php/smarty/pull/586)
+- Bug fix for underscore and limited length in template name in custom resources [#581](https://github.com/smarty-php/smarty/pull/581)
 
 ## [4.2.1] - 2022-09-14
 
diff --git a/libs/sysplugins/smarty_resource_custom.php b/libs/sysplugins/smarty_resource_custom.php
index b2872674..d2a945aa 100644
--- a/libs/sysplugins/smarty_resource_custom.php
+++ b/libs/sysplugins/smarty_resource_custom.php
@@ -47,7 +47,7 @@ abstract class Smarty_Resource_Custom extends Smarty_Resource
      */
     public function populate(Smarty_Template_Source $source, Smarty_Internal_Template $_template = null)
     {
-        $source->filepath = $source->type . ':' . substr(preg_replace('/[^A-Za-z0-9._]/', '', $source->name), 0, 255);
+        $source->filepath = $source->type . ':' . substr(preg_replace('/[^A-Za-z0-9._]/', '', $source->name), 0, 127);
         $source->uid = sha1($source->type . ':' . $source->name);
         $mtime = $this->fetchTimestamp($source->name);
         if ($mtime !== null) {
@@ -88,6 +88,6 @@ abstract class Smarty_Resource_Custom extends Smarty_Resource
      */
     public function getBasename(Smarty_Template_Source $source)
     {
-        return basename(substr(preg_replace('/[^A-Za-z0-9._]/', '', $source->name), 0, 255));
+        return basename(substr(preg_replace('/[^A-Za-z0-9._]/', '', $source->name), 0, 127));
     }
 }