diff --git a/gateway/platforms/api_server.py b/gateway/platforms/api_server.py
index dc60887459..f1def35d9c 100644
--- a/gateway/platforms/api_server.py
+++ b/gateway/platforms/api_server.py
@@ -62,6 +62,14 @@ MAX_NORMALIZED_TEXT_LENGTH = 65_536  # 64 KB cap for normalized content parts
 MAX_CONTENT_LIST_SIZE = 1_000  # Max items when content is an array
 
 
+def _coerce_port(value: Any, default: int = DEFAULT_PORT) -> int:
+    """Parse a listen port without letting malformed env/config values crash startup."""
+    try:
+        return int(value)
+    except (TypeError, ValueError):
+        return default
+
+
 def _normalize_chat_content(
     content: Any, *, _max_depth: int = 10, _depth: int = 0,
 ) -> str:
@@ -573,7 +581,10 @@ class APIServerAdapter(BasePlatformAdapter):
         super().__init__(config, Platform.API_SERVER)
         extra = config.extra or {}
         self._host: str = extra.get("host", os.getenv("API_SERVER_HOST", DEFAULT_HOST))
-        self._port: int = int(extra.get("port", os.getenv("API_SERVER_PORT", str(DEFAULT_PORT))))
+        raw_port = extra.get("port")
+        if raw_port is None:
+            raw_port = os.getenv("API_SERVER_PORT", str(DEFAULT_PORT))
+        self._port: int = _coerce_port(raw_port, DEFAULT_PORT)
         self._api_key: str = extra.get("key", os.getenv("API_SERVER_KEY", ""))
         self._cors_origins: tuple[str, ...] = self._parse_cors_origins(
             extra.get("cors_origins", os.getenv("API_SERVER_CORS_ORIGINS", "")),
diff --git a/tests/gateway/test_api_server.py b/tests/gateway/test_api_server.py
index 74a30541dc..0bc2d043e3 100644
--- a/tests/gateway/test_api_server.py
+++ b/tests/gateway/test_api_server.py
@@ -240,6 +240,12 @@ class TestAdapterInit:
             "http://127.0.0.1:3000",
         )
 
+    def test_invalid_port_from_env_falls_back_to_default(self, monkeypatch):
+        monkeypatch.setenv("API_SERVER_PORT", "not-a-port")
+        config = PlatformConfig(enabled=True)
+        adapter = APIServerAdapter(config)
+        assert adapter._port == 8642
+
 
 # ---------------------------------------------------------------------------
 # Auth checking