diff --git a/duniterpy/api/endpoint.py b/duniterpy/api/endpoint.py
index f48020c21e2d38f26bd48f4314d05747c913fcfe..c6f0e07742f399bda23df31d0acf29bfa1750cdc 100644
--- a/duniterpy/api/endpoint.py
+++ b/duniterpy/api/endpoint.py
@@ -456,7 +456,7 @@ ESUserEndpointType = TypeVar("ESUserEndpointType", bound="ESUserEndpoint")
 class ESUserEndpoint(Endpoint):
     API = "ES_USER_API"
     re_inline = re.compile(
-        "^{API} (?P<host>(?:{const.HOST_REGEX})|(?:{const.IPV4_REGEX})) (?P<port>{const.PORT_REGEX})$"
+        f"^{API} (?P<host>(?:{const.HOST_REGEX})|(?:{const.IPV4_REGEX})) (?P<port>{const.PORT_REGEX})$"
     )
 
     def __init__(self, host: str, port: int) -> None: