diff --git a/README.md b/README.md
index b744ad198..23655ed0d 100644
--- a/README.md
+++ b/README.md
@@ -55,6 +55,10 @@ It means that composer will look at `master` branch of repository configured und
 
 ## Changelog
 
+### 2024-02-02
+
+- `str_len` deprecation warning fix in CakeResponse (passing null instead of `string`)
+
 ### 2024-01-19
 
 - `strotime()` and `preg_split()` in CakeResponse deprecation warning fixes (passing null)
diff --git a/lib/Cake/Network/CakeResponse.php b/lib/Cake/Network/CakeResponse.php
index adf0ab72b..6ad28da51 100644
--- a/lib/Cake/Network/CakeResponse.php
+++ b/lib/Cake/Network/CakeResponse.php
@@ -516,7 +516,7 @@ class CakeResponse {
 			if (ini_get('mbstring.func_overload') & 2 && function_exists('mb_strlen')) {
 				$this->length($offset + mb_strlen($this->_body, '8bit'));
 			} else {
-				$this->length($this->_headers['Content-Length'] = $offset + strlen($this->_body));
+				$this->length($this->_headers['Content-Length'] = $offset + ($this->_body === null ? 0 : strlen($this->_body)));
 			}
 		}
 	}