diff --git a/exchangelib/util.py b/exchangelib/util.py
index 17f6220c..bc7c8fb3 100644
--- a/exchangelib/util.py
+++ b/exchangelib/util.py
@@ -516,7 +516,10 @@ def post_ratelimited(protocol, session, url, headers, data, allow_redirects=Fals
             except UnicodeDecodeError:
                 import chardet
                 encoding_info = chardet.detect(data)
-                data = data.decode('utf-8').encode(encoding_info['encoding'])
+                if encoding_info['encoding'] in ['ISO-8859-1', 'Windows-1252']:
+                    data = data.decode("utf-8").encode("utf-8")
+                else:
+                    data = data.decode('utf-8').encode(encoding_info['encoding'])
             try:
                 r = session.post(url=url,
                                  headers=headers,