diff --git a/src/nwp500/auth.py b/src/nwp500/auth.py
index a71f39b..fadd188 100644
--- a/src/nwp500/auth.py
+++ b/src/nwp500/auth.py
@@ -367,7 +367,7 @@ def __init__(
     async def __aenter__(self) -> "NavienAuthClient":
         """Async context manager entry."""
         if self._owned_session:
-            self._session = aiohttp.ClientSession(timeout=self.timeout)
+            self._session = self._create_session()
 
         # Check if we have valid stored tokens
         if self._auth_response and self._auth_response.tokens:
@@ -394,10 +394,24 @@ async def __aexit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
         if self._owned_session and self._session:
             await self._session.close()
 
+    def _create_session(self) -> aiohttp.ClientSession:
+        """Create an aiohttp ClientSession with ThreadedResolver.
+
+        ThreadedResolver uses Python's built-in socket module for DNS
+        resolution, avoiding dependency on c-ares which can fail in
+        containerized environments.
+
+        Returns:
+            aiohttp.ClientSession configured with ThreadedResolver
+        """
+        resolver = aiohttp.ThreadedResolver()
+        connector = aiohttp.TCPConnector(resolver=resolver)
+        return aiohttp.ClientSession(connector=connector, timeout=self.timeout)
+
     async def _ensure_session(self) -> None:
         """Ensure we have an active session."""
         if self._session is None:
-            self._session = aiohttp.ClientSession(timeout=self.timeout)
+            self._session = self._create_session()
             self._owned_session = True
 
     async def sign_in(
@@ -740,8 +754,11 @@ async def refresh_access_token(refresh_token: str) -> AuthTokens:
     url = f"{API_BASE_URL}{REFRESH_ENDPOINT}"
     payload = {"refreshToken": refresh_token}
 
+    # Use ThreadedResolver for reliable DNS in containerized environments
+    resolver = aiohttp.ThreadedResolver()
+    connector = aiohttp.TCPConnector(resolver=resolver)
     async with (
-        aiohttp.ClientSession() as session,
+        aiohttp.ClientSession(connector=connector) as session,
         session.post(url, json=payload) as response,
     ):
         response_data = await response.json()