diff --git a/HISTORY.rst b/HISTORY.rst
index 47c0617..bc99679 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -10,6 +10,10 @@ History
 * The version is now retrieved from package metadata at runtime using
   ``importlib.metadata``. This reduces the chance of version inconsistencies
   during releases.
+* The async client now builds its ``Authorization`` header with
+  ``aiohttp.encode_basic_auth()`` instead of the ``aiohttp.BasicAuth`` /
+  ``auth=`` parameter, which are deprecated as of aiohttp 3.14.0. As a result,
+  the minimum required ``aiohttp`` version is now 3.14.0.
 
 5.2.0 (2025-11-20)
 ++++++++++++++++++
diff --git a/src/geoip2/webservice.py b/src/geoip2/webservice.py
index 55899f1..924854d 100644
--- a/src/geoip2/webservice.py
+++ b/src/geoip2/webservice.py
@@ -354,8 +354,14 @@ async def insights(self, ip_address: IPAddress = "me") -> Insights:
     async def _session(self) -> aiohttp.ClientSession:
         if not hasattr(self, "_existing_session"):
             self._existing_session = aiohttp.ClientSession(
-                auth=aiohttp.BasicAuth(self._account_id, self._license_key),
-                headers={"Accept": "application/json", "User-Agent": _AIOHTTP_UA},
+                headers={
+                    "Accept": "application/json",
+                    "Authorization": aiohttp.encode_basic_auth(
+                        self._account_id,
+                        self._license_key,
+                    ),
+                    "User-Agent": _AIOHTTP_UA,
+                },
                 timeout=aiohttp.ClientTimeout(total=self._timeout),
             )