diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9c58ff21..492defd4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Fixed PHP8.1 deprecation errors in modifiers (upper, explode, number_format and replace) [#755](https://github.com/smarty-php/smarty/pull/755) and [#788](https://github.com/smarty-php/smarty/pull/788)
+
 ## [4.2.0] - 2022-08-01
 
 ### Fixed
diff --git a/libs/plugins/modifiercompiler.upper.php b/libs/plugins/modifiercompiler.upper.php
index e12ae676..31a90a05 100644
--- a/libs/plugins/modifiercompiler.upper.php
+++ b/libs/plugins/modifiercompiler.upper.php
@@ -21,8 +21,8 @@
 function smarty_modifiercompiler_upper($params)
 {
     if (Smarty::$_MBSTRING) {
-        return 'mb_strtoupper(' . $params[ 0 ] . ', \'' . addslashes(Smarty::$_CHARSET) . '\')';
+        return 'mb_strtoupper(' . $params[ 0 ] . ' ?? \'\', \'' . addslashes(Smarty::$_CHARSET) . '\')';
     }
     // no MBString fallback
-    return 'strtoupper(' . $params[ 0 ] . ')';
+    return 'strtoupper(' . $params[ 0 ] . ' ?? \'\')';
 }