diff --git a/httpie/client.py b/httpie/client.py
index d9a46d6f..788a56c2 100644
--- a/httpie/client.py
+++ b/httpie/client.py
@@ -12,6 +12,7 @@ import requests
 import urllib3
 from . import __version__
 from .cli.dicts import RequestHeadersDict
+from .constants import UTF8
 from .plugins.registry import plugin_manager
 from .sessions import get_httpie_session
 from .ssl import AVAILABLE_SSL_VERSION_ARG_MAPPING, HTTPieHTTPSAdapter
@@ -24,7 +25,7 @@ from .utils import get_expired_cookies, repr_dict
 
 urllib3.disable_warnings()
 
-FORM_CONTENT_TYPE = 'application/x-www-form-urlencoded; charset=UTF-8'
+FORM_CONTENT_TYPE = f'application/x-www-form-urlencoded; charset={UTF8}'
 JSON_CONTENT_TYPE = 'application/json'
 JSON_ACCEPT = f'{JSON_CONTENT_TYPE}, */*;q=0.5'
 DEFAULT_UA = f'HTTPie/{__version__}'