diff --git a/onnxscript/optimizer/_constant_folding.py b/onnxscript/optimizer/_constant_folding.py
index 4053bb2a1..c9a61475f 100644
--- a/onnxscript/optimizer/_constant_folding.py
+++ b/onnxscript/optimizer/_constant_folding.py
@@ -242,10 +242,12 @@ def _get_numpy_value(val: ir.Value | None) -> np.ndarray | None:
     const_value = val.const_value
     if const_value is not None:
         try:
-            return const_value.numpy()
+            array = const_value.numpy()
         except FileNotFoundError:
             # External data is not available.
             return None
+        assert isinstance(array, np.ndarray)
+        return array
     return None
 
 
@@ -255,14 +257,7 @@ def _get_bool_value(val: ir.Value | None) -> bool | None:
     value = _get_numpy_value(val)
     if value is None:
         return None
-    # TODO: cleanup following checks, which seem redundant. But need to also ensure
-    # the invariant when setting the value (and also use clearly defined representation
-    # types in evaluators, such a reference-evaluator).
-    if isinstance(value, bool):
-        return value
-    if isinstance(value, np.bool_):
-        return bool(value)
-    if isinstance(value, np.ndarray) and value.size == 1 and value.dtype == bool:
+    if value.size == 1 and value.dtype is bool:
         return value.item(0)
     return None
 
diff --git a/onnxscript/rewriter/broadcast_to_matmul.py b/onnxscript/rewriter/broadcast_to_matmul.py
index df216d977..4ce77c855 100644
--- a/onnxscript/rewriter/broadcast_to_matmul.py
+++ b/onnxscript/rewriter/broadcast_to_matmul.py
@@ -55,7 +55,7 @@ def check_if_not_need_reshape(
         return False
     input_a_shape = input_a_shape.numpy()  # type: ignore[assignment]
     input_b_shape = input_b_shape.numpy()  # type: ignore[assignment]
-    shape_c = shape_c_tensor.numpy().tolist()
+    shape_c = shape_c_tensor.numpy().tolist()  # type: ignore[assignment]
 
     a_rank = len(input_a_shape)
     b_rank = len(input_b_shape)
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 103fab8ab..466de2c71 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,5 +1,5 @@
 setuptools>=61.0.0
-numpy
+numpy<2.2
 onnx-weekly>=1.17.0.dev20240325
 onnxruntime>=1.17.0
 typing_extensions