diff --git a/pyproject.toml b/pyproject.toml
index e454cc9..e280201 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -62,3 +62,8 @@ dev = [
 ]
 [project.scripts]
 mllam_data_prep = "mllam_data_prep:cli.call"
+
+[tool.pytest.ini_options]
+markers = [
+    "slow: marks tests requiring network access or AWS credentials (deselect with '-m \"not slow\"')",
+]
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 064bbba..bd4a47f 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -1,3 +1,4 @@
+import subprocess
 import tempfile
 
 import pytest
@@ -6,9 +7,20 @@
 from mllam_data_prep.cli import call
 
 
+@pytest.mark.slow
 @pytest.mark.parametrize("args", [["example.danra.yaml"]])
 def test_call(args):
     with tempfile.TemporaryDirectory(suffix=".zarr") as tmpdir:
         args.extend(["--output", tmpdir])
         call(args)
         _ = xr.open_zarr(tmpdir)
+
+
+def test_cli_entrypoint_help():
+    """Test the actual installed CLI entry point works as a subprocess."""
+    result = subprocess.run(
+        ["mllam_data_prep", "--help"],
+        capture_output=True, text=True
+    )
+    assert result.returncode == 0
+    assert "config" in result.stdout.lower()