diff --git a/scripts/odysseus-cookbook b/scripts/odysseus-cookbook
index 845a2db..860a790 100755
--- a/scripts/odysseus-cookbook
+++ b/scripts/odysseus-cookbook
@@ -411,6 +411,8 @@ def cmd_state_set(args) -> None:
         obj = json.loads(data)
     except json.JSONDecodeError as e:
         fail(f"invalid JSON on stdin: {e}")
+    if not isinstance(obj, dict):
+        fail("invalid cookbook state: expected a JSON object")
     _STATE_PATH.parent.mkdir(parents=True, exist_ok=True)
     # Backup the existing state — undo button if a bad pipe clobbers it.
     if _STATE_PATH.exists():
diff --git a/tests/test_cookbook_cli_state.py b/tests/test_cookbook_cli_state.py
new file mode 100644
index 0000000..5673d5d
--- /dev/null
+++ b/tests/test_cookbook_cli_state.py
@@ -0,0 +1,30 @@
+import importlib.machinery
+import importlib.util
+import io
+from pathlib import Path
+
+import pytest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def _load_cli():
+    path = ROOT / "scripts" / "odysseus-cookbook"
+    loader = importlib.machinery.SourceFileLoader("odysseus_cookbook_cli", str(path))
+    spec = importlib.util.spec_from_loader(loader.name, loader)
+    module = importlib.util.module_from_spec(spec)
+    loader.exec_module(module)
+    return module
+
+
+def test_state_set_rejects_non_object_json(tmp_path, monkeypatch, capsys):
+    cli = _load_cli()
+    cli._STATE_PATH = tmp_path / "cookbook_state.json"
+    monkeypatch.setattr(cli.sys, "stdin", io.StringIO("[]"))
+
+    with pytest.raises(SystemExit):
+        cli.cmd_state_set(type("Args", (), {})())
+
+    assert "expected a JSON object" in capsys.readouterr().err
+    assert not cli._STATE_PATH.exists()