diff --git a/CHANGES.rst b/CHANGES.rst
index edac84affb..bf71854c4b 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -38,6 +38,7 @@ https://github.com/zopefoundation/Zope/blob/4.x/CHANGES.rst
   For details, see
   `#1202 <https://github.com/zopefoundation/Zope/issues/1202>`_.
 
+- Small optimization when encoding the response body.
 
 5.9 (2023-11-24)
 ----------------
diff --git a/src/ZPublisher/HTTPResponse.py b/src/ZPublisher/HTTPResponse.py
index 264a488a03..9967cd9b8f 100644
--- a/src/ZPublisher/HTTPResponse.py
+++ b/src/ZPublisher/HTTPResponse.py
@@ -552,7 +552,9 @@ def setBody(self, body, title='', is_error=False, lock=None):
             except (TypeError, UnicodeError):
                 pass
         if not isinstance(body, bytes):
-            body = self._encode_unicode(str(body))
+            if not isinstance(body, str):
+                body = str(body)
+            body = self._encode_unicode(body)
 
         # At this point body is always binary
         b_len = len(body)