diff --git a/bincio/extract/writer.py b/bincio/extract/writer.py
index f4bd98d..512b263 100644
--- a/bincio/extract/writer.py
+++ b/bincio/extract/writer.py
@@ -382,7 +382,9 @@ def write_athlete_json(summaries: list[dict], output_dir: Path, athlete_config:
         **athlete_config,
     }
     (output_dir / "athlete.json").write_text(
-        json.dumps(athlete, indent=2, ensure_ascii=False)
+        json.dumps(athlete, indent=2, ensure_ascii=False),
+        encoding="utf-8",
+        errors="replace",
     )
 
 
diff --git a/bincio/serve/routers/activities.py b/bincio/serve/routers/activities.py
index 143021b..2cc36fa 100644
--- a/bincio/serve/routers/activities.py
+++ b/bincio/serve/routers/activities.py
@@ -285,7 +285,10 @@ async def get_athlete(bincio_session: str | None = Cookie(default=None)) -> JSON
     athlete_path = dd / "athlete.json"
     data: dict = {}
     if athlete_path.exists():
-        data = json.loads(athlete_path.read_text(encoding="utf-8"))
+        try:
+            data = json.loads(athlete_path.read_text(encoding="utf-8"))
+        except (json.JSONDecodeError, OSError):
+            pass
     # Layer edits/athlete.yaml on top
     edits_path = dd / "edits" / "athlete.yaml"
     if edits_path.exists():