diff --git a/sdk/python/src/codex_app_server/client.py b/sdk/python/src/codex_app_server/client.py
index aa7b574a3..146d5186e 100644
--- a/sdk/python/src/codex_app_server/client.py
+++ b/sdk/python/src/codex_app_server/client.py
@@ -181,6 +181,7 @@ class AppServerClient:
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             text=True,
+            encoding="utf-8",
             cwd=self.config.cwd,
             env=env,
             bufsize=1,