diff --git a/promptlens/cli.py b/promptlens/cli.py
index 235963a..9348304 100644
--- a/promptlens/cli.py
+++ b/promptlens/cli.py
@@ -27,6 +27,17 @@
 console = Console()
 
 
+def _normalize_config_data(config_data: object, config_path: str) -> dict:
+    """Validate and normalize loaded YAML config payload."""
+    if config_data is None:
+        raise ValueError(f"Configuration file is empty: {config_path}")
+    if not isinstance(config_data, dict):
+        raise ValueError(
+            f"Invalid configuration format in {config_path}: expected a YAML mapping at top level"
+        )
+    return config_data
+
+
 def _remove_path_if_exists(path: Path) -> None:
     """Remove a file/symlink/directory path if it exists."""
     if path.is_symlink() or path.is_file():
@@ -100,7 +111,7 @@ def run(
         # Load config
         console.print(f"\n[cyan]Loading configuration from {config}...[/cyan]")
         with open(config, "r") as f:
-            config_data = yaml.safe_load(f)
+            config_data = _normalize_config_data(yaml.safe_load(f), config)
 
         # Override with CLI options
         if golden_set:
diff --git a/tests/test_cli_config_shape_validation.py b/tests/test_cli_config_shape_validation.py
new file mode 100644
index 0000000..384e8d4
--- /dev/null
+++ b/tests/test_cli_config_shape_validation.py
@@ -0,0 +1,18 @@
+import pytest
+
+from promptlens.cli import _normalize_config_data
+
+
+def test_normalize_config_data_rejects_empty_config() -> None:
+    with pytest.raises(ValueError, match="Configuration file is empty"):
+        _normalize_config_data(None, "config.yaml")
+
+
+def test_normalize_config_data_rejects_non_mapping() -> None:
+    with pytest.raises(ValueError, match="expected a YAML mapping at top level"):
+        _normalize_config_data([{"golden_set": "tests.yaml"}], "config.yaml")
+
+
+def test_normalize_config_data_accepts_mapping() -> None:
+    data = {"golden_set": "tests.yaml", "models": []}
+    assert _normalize_config_data(data, "config.yaml") == data