diff --git a/hate_crack/noninteractive.py b/hate_crack/noninteractive.py
index 154e615..9790fdb 100644
--- a/hate_crack/noninteractive.py
+++ b/hate_crack/noninteractive.py
@@ -10,7 +10,7 @@ import os
 from typing import Any
 
 
-def build_rule_chains(ctx: Any, rule_tokens):
+def build_rule_chains(ctx: Any, rule_tokens: list[str] | None) -> list[str]:
     """Convert CLI ``--rules`` tokens into hashcat ``-r`` chain strings.
 
     Each token becomes one attack pass. A token may chain multiple rule files
@@ -34,5 +34,7 @@ def build_rule_chains(ctx: Any, rule_tokens):
             if not os.path.isfile(path):
                 raise FileNotFoundError(name)
             chain = f"{chain} -r {path}".strip()
+        if not chain:
+            raise ValueError(f"Rule token {token!r} resolved to no rule files")
         chains.append(chain)
     return chains
diff --git a/tests/test_noninteractive.py b/tests/test_noninteractive.py
index 194e801..3fd50e8 100644
--- a/tests/test_noninteractive.py
+++ b/tests/test_noninteractive.py
@@ -38,10 +38,18 @@ def test_build_rule_chains_chained_token(tmp_path):
 def test_build_rule_chains_multiple_tokens_are_separate_passes(tmp_path):
     ctx = _ctx_with_rules(tmp_path, "best64.rule", "d3ad0ne.rule")
     chains = ni.build_rule_chains(ctx, ["best64.rule", "d3ad0ne.rule"])
-    assert len(chains) == 2
+    a = os.path.join(ctx.rulesDirectory, "best64.rule")
+    b = os.path.join(ctx.rulesDirectory, "d3ad0ne.rule")
+    assert chains == [f"-r {a}", f"-r {b}"]
 
 
 def test_build_rule_chains_missing_file_raises(tmp_path):
     ctx = _ctx_with_rules(tmp_path)
-    with pytest.raises(FileNotFoundError):
+    with pytest.raises(FileNotFoundError, match="nope.rule"):
         ni.build_rule_chains(ctx, ["nope.rule"])
+
+
+def test_build_rule_chains_empty_token_raises(tmp_path):
+    ctx = _ctx_with_rules(tmp_path, "best64.rule")
+    with pytest.raises(ValueError):
+        ni.build_rule_chains(ctx, ["+"])