diff --git a/promptlens/loaders/json_loader.py b/promptlens/loaders/json_loader.py
index d18d69d..a240336 100644
--- a/promptlens/loaders/json_loader.py
+++ b/promptlens/loaders/json_loader.py
@@ -36,6 +36,11 @@ def load(self, path: str) -> GoldenSet:
         except json.JSONDecodeError as e:
             raise ValueError(f"Invalid JSON in {path}: {e}")
 
+        if not isinstance(data, dict):
+            raise ValueError(
+                f"Invalid golden set format in {path}: root value must be a JSON object"
+            )
+
         try:
             golden_set = GoldenSet(**data)
             logger.info(
diff --git a/promptlens/loaders/yaml_loader.py b/promptlens/loaders/yaml_loader.py
index e24365f..6a1a13e 100644
--- a/promptlens/loaders/yaml_loader.py
+++ b/promptlens/loaders/yaml_loader.py
@@ -39,6 +39,11 @@ def load(self, path: str) -> GoldenSet:
         if data is None:
             raise ValueError(f"Empty YAML file: {path}")
 
+        if not isinstance(data, dict):
+            raise ValueError(
+                f"Invalid golden set format in {path}: root value must be a YAML mapping"
+            )
+
         try:
             golden_set = GoldenSet(**data)
             logger.info(
diff --git a/tests/test_loader_root_validation.py b/tests/test_loader_root_validation.py
new file mode 100644
index 0000000..3760b00
--- /dev/null
+++ b/tests/test_loader_root_validation.py
@@ -0,0 +1,22 @@
+import json
+
+import pytest
+
+from promptlens.loaders.json_loader import JSONLoader
+from promptlens.loaders.yaml_loader import YAMLLoader
+
+
+def test_json_loader_rejects_non_object_root(tmp_path):
+    p = tmp_path / "golden.json"
+    p.write_text(json.dumps([{"id": "tc-1"}]), encoding="utf-8")
+
+    with pytest.raises(ValueError, match="root value must be a JSON object"):
+        JSONLoader().load(str(p))
+
+
+def test_yaml_loader_rejects_non_mapping_root(tmp_path):
+    p = tmp_path / "golden.yaml"
+    p.write_text("- id: tc-1\n", encoding="utf-8")
+
+    with pytest.raises(ValueError, match="root value must be a YAML mapping"):
+        YAMLLoader().load(str(p))