diff --git a/setup.cfg b/setup.cfg
index c1060e5..b24a570 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -26,7 +26,6 @@ packages = find:
 package_dir =
     = src
 install_requires =
-    numba
     numpy
     colorama
     tqdm
@@ -41,6 +40,7 @@ console_scripts =
 [options.extras_require]
 decision =
     graphviz
+    numba
 
 dev = 
     black
diff --git a/src/doddle/cli.py b/src/doddle/cli.py
index 24d3f11..d7cb61a 100644
--- a/src/doddle/cli.py
+++ b/src/doddle/cli.py
@@ -91,7 +91,7 @@ def main() -> None:
 def parse_args(args: Sequence[str]) -> None:
 
     parser = ArgumentParser()
-    subparsers = parser.add_subparsers()
+    subparsers = parser.add_subparsers(required=True)
 
     run_parser = subparsers.add_parser("run")
     run_parser.add_argument("--answer", required=True, type=Word)
@@ -124,4 +124,8 @@ def parse_args(args: Sequence[str]) -> None:
     benchmark_parser.set_defaults(func=benchmark_performance)
 
     namespace = parser.parse_args(args)
+    if not hasattr(namespace, "func"):
+        parser.print_help()
+        return
+
     namespace.func(namespace)
diff --git a/src/doddle/histogram.py b/src/doddle/histogram.py
index 8937595..5364ddb 100644
--- a/src/doddle/histogram.py
+++ b/src/doddle/histogram.py
@@ -5,7 +5,6 @@
 from typing import Callable, Iterator, TypeVar
 
 import numpy as np
-from numba import njit  # type: ignore
 
 from .guess import Guess
 from .scoring import Scorer
@@ -134,7 +133,6 @@ def to_histogram(solns_by_score: dict[int, WordSeries]) -> np.ndarray:
     return vector
 
 
-@njit
 def _populate_histogram(matrix: np.ndarray, row: int, hist: np.ndarray) -> bool:
     """Aggressive optimisation of the histogram creation.
 
diff --git a/src/doddle/scoring.py b/src/doddle/scoring.py
index 4b63610..e0e8ca3 100644
--- a/src/doddle/scoring.py
+++ b/src/doddle/scoring.py
@@ -1,5 +1,4 @@
 import numpy as np
-from numba import int8, int32, jit  # type: ignore
 
 from .words import Word
 
@@ -72,7 +71,6 @@ def score_word(self, solution: Word, guess: Word) -> int:
         return _score_word_jit(solution.vector, guess.vector, self._powers)
 
 
-@jit(int32(int8[:], int8[:], int32[:]), nopython=True)
 def _score_word_jit(solution_array: np.ndarray, guess_array: np.ndarray, powers: np.ndarray) -> int:
     """Optimised internal call to score a word. See Solver.score_word(...) for details."""
 
diff --git a/src/doddle/words.py b/src/doddle/words.py
index 6091a0a..772d6ef 100644
--- a/src/doddle/words.py
+++ b/src/doddle/words.py
@@ -153,7 +153,7 @@ def __find_index(self, value: str | Word) -> int:
     def __getitem__(self, s: slice | np.ndarray) -> WordSeries:
 
         is_slice = isinstance(s, slice)
-        is_mask = isinstance(s, np.ndarray) and s.dtype == np.bool8
+        is_mask = isinstance(s, np.ndarray) and s.dtype == np.bool_
         is_index = isinstance(s, np.ndarray) and s.dtype == np.int_
         can_index = is_slice or is_mask or is_index