diff --git a/backend/packages/harness/deerflow/models/credential_loader.py b/backend/packages/harness/deerflow/models/credential_loader.py
index 9e16c43c3..05f839ed1 100644
--- a/backend/packages/harness/deerflow/models/credential_loader.py
+++ b/backend/packages/harness/deerflow/models/credential_loader.py
@@ -160,10 +160,15 @@ def _extract_claude_code_credential(data: dict[str, Any], source: str) -> Claude
         logger.debug("Claude Code credentials container exists but no accessToken found")
         return None
 
+    expires_at = oauth.get("expiresAt", 0)
+    if not isinstance(expires_at, (int, float)):
+        logger.debug("Claude Code credentials source %s has a non-numeric expiresAt; skipping", source)
+        return None
+
     cred = ClaudeCodeCredential(
         access_token=access_token,
         refresh_token=oauth.get("refreshToken", ""),
-        expires_at=oauth.get("expiresAt", 0),
+        expires_at=expires_at,
         source=source,
     )
 
diff --git a/backend/tests/test_credential_loader.py b/backend/tests/test_credential_loader.py
index b9a1b4580..2df804f68 100644
--- a/backend/tests/test_credential_loader.py
+++ b/backend/tests/test_credential_loader.py
@@ -300,6 +300,62 @@ def test_load_claude_code_credential_falls_back_to_default_when_override_contain
     assert cred.source == "claude-cli-file"
 
 
+@pytest.mark.parametrize(
+    "expires_at",
+    [
+        "1773430695128",
+        None,
+        [],
+        {},
+    ],
+)
+def test_load_claude_code_credential_ignores_non_numeric_expires_at(tmp_path, monkeypatch, expires_at):
+    _clear_claude_code_env(monkeypatch)
+    monkeypatch.setenv("HOME", str(tmp_path))
+    cred_file = tmp_path / "credentials.json"
+    cred_file.write_text(
+        json.dumps({"claudeAiOauth": {"accessToken": "sk-ant-oat01-test", "expiresAt": expires_at}}),
+        encoding="utf-8",
+    )
+    monkeypatch.setenv("CLAUDE_CODE_CREDENTIALS_PATH", str(cred_file))
+
+    assert load_claude_code_credential() is None
+
+
+def test_load_claude_code_credential_falls_back_to_default_when_override_expires_at_is_non_numeric(tmp_path, monkeypatch):
+    _clear_claude_code_env(monkeypatch)
+    monkeypatch.setenv("HOME", str(tmp_path))
+
+    override_path = tmp_path / "credentials.json"
+    override_path.write_text(
+        json.dumps({"claudeAiOauth": {"accessToken": "sk-ant-oat01-override", "expiresAt": "1773430695128"}}),
+        encoding="utf-8",
+    )
+    monkeypatch.setenv("CLAUDE_CODE_CREDENTIALS_PATH", str(override_path))
+
+    default_path = tmp_path / ".claude" / ".credentials.json"
+    default_path.parent.mkdir()
+    default_path.write_text(
+        json.dumps(
+            {
+                "claudeAiOauth": {
+                    "accessToken": "sk-ant-oat01-default",
+                    "refreshToken": "sk-ant-ort01-default",
+                    "expiresAt": 4_102_444_800_000,
+                }
+            }
+        ),
+        encoding="utf-8",
+    )
+
+    cred = load_claude_code_credential()
+
+    assert cred is not None
+    assert cred.access_token == "sk-ant-oat01-default"
+    assert cred.refresh_token == "sk-ant-ort01-default"
+    assert cred.source == "claude-cli-file"
+
+
 def test_load_codex_cli_credential_supports_nested_tokens_shape(tmp_path, monkeypatch):
     auth_path = tmp_path / "auth.json"
     auth_path.write_text(