diff --git a/src/leakgauge/cli.py b/src/leakgauge/cli.py
index cd5ae02..8e3860d 100644
--- a/src/leakgauge/cli.py
+++ b/src/leakgauge/cli.py
@@ -126,6 +126,14 @@ def _run(argv: list[str]) -> int:
         print(f"[leakgauge] --max-steps must be >= 1 (got {args.max_steps})", file=sys.stderr)
         return 2
 
+    if args.k < 1:
+        print(f"[leakgauge] --k must be >= 1 (got {args.k})", file=sys.stderr)
+        return 2
+
+    if args.seed < 0:
+        print(f"[leakgauge] --seed must be >= 0 (got {args.seed})", file=sys.stderr)
+        return 2
+
     selected: list[Case] | None = None
     suite_label = args.suite
     if args.case is not None:
diff --git a/tests/test_cli_validation.py b/tests/test_cli_validation.py
new file mode 100644
index 0000000..2e230ad
--- /dev/null
+++ b/tests/test_cli_validation.py
@@ -0,0 +1,33 @@
+"""--k and --seed are validated before a run starts, so a degenerate value
+(zero repeats, negative seed) fails with a clear message instead of a confusing
+empty run downstream."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from leakgauge.cli import main
+
+
+def test_k_zero_errors_cleanly(tmp_path: Path) -> None:
+    rc = main(["--k", "0", "--results-dir", str(tmp_path)])
+    assert rc == 2
+    assert not (tmp_path / "stub_demo.json").exists()  # nothing written on error
+
+
+def test_k_negative_errors_cleanly(tmp_path: Path) -> None:
+    rc = main(["--k", "-1", "--results-dir", str(tmp_path)])
+    assert rc == 2
+    assert not (tmp_path / "stub_demo.json").exists()
+
+
+def test_seed_negative_errors_cleanly(tmp_path: Path) -> None:
+    rc = main(["--seed", "-1", "--results-dir", str(tmp_path)])
+    assert rc == 2
+    assert not (tmp_path / "stub_demo.json").exists()
+
+
+def test_valid_k_and_seed_still_run(tmp_path: Path) -> None:
+    rc = main(["--k", "2", "--seed", "0", "--results-dir", str(tmp_path)])
+    assert rc == 0
+    assert (tmp_path / "stub_demo.json").exists()