diff --git a/src/pypcd4/pypcd4.py b/src/pypcd4/pypcd4.py
index f1bfaf4..cf47b77 100644
--- a/src/pypcd4/pypcd4.py
+++ b/src/pypcd4/pypcd4.py
@@ -7,9 +7,9 @@
 from enum import Enum
 from io import BufferedReader
 from pathlib import Path
-from typing import TYPE_CHECKING, BinaryIO, List, Literal, Optional, Sequence, Tuple, Union
+from typing import TYPE_CHECKING, BinaryIO, List, Literal, Optional, Sequence, Tuple, Union, cast
 
-import lzf
+import lzf  # type: ignore
 import numpy as np
 import numpy.typing as npt
 from pydantic import BaseModel, NonNegativeInt, PositiveInt
@@ -21,8 +21,8 @@
 )
 
 if TYPE_CHECKING:
-    from sensor_msgs.msg import PointCloud2
-    from std_msgs.msg import Header
+    from sensor_msgs.msg import PointCloud2  # type: ignore
+    from std_msgs.msg import Header  # type: ignore
 
 PathLike = Union[str, Path]
 
@@ -207,7 +207,7 @@ def _parse_pc_data(fp: BufferedReader, metadata: MetaData) -> npt.NDArray:
 def _compose_pc_data(
     points: Union[npt.NDArray, Sequence[npt.NDArray]], metadata: MetaData
 ) -> npt.NDArray:
-    arrays: Sequence[npt.NDArray] = tuple(points.T) if isinstance(points, np.ndarray) else points
+    arrays = tuple(points.T) if isinstance(points, np.ndarray) else points
 
     return np.rec.fromarrays(arrays, dtype=metadata.build_dtype())
 
@@ -616,30 +616,30 @@ def to_msg(self, header: Optional["Header"] = None) -> "PointCloud2":
         """
         ROS_MSG_AVAILABLE = False
         try:
-            from sensor_msgs.msg import PointCloud2, PointField
-            from std_msgs.msg import Header
+            from sensor_msgs.msg import PointCloud2, PointField  # type: ignore
+            from std_msgs.msg import Header  # type: ignore
 
             ROS_MSG_AVAILABLE = True
             try:
-                from builtin_interfaces.msg import Time  # ROS2
+                from builtin_interfaces.msg import Time  # ROS2  # type: ignore
             except ImportError:
-                from std_msgs.msg import Time  # ROS1
+                from std_msgs.msg import Time  # ROS1  # type: ignore
         except ImportError:
             pass
 
         if not ROS_MSG_AVAILABLE:
             try:
                 # Fallback to rosbags
-                from rosbags.typesys.stores.latest import (
+                from rosbags.typesys.stores.latest import (  # type: ignore
                     builtin_interfaces__msg__Time as Time,
                 )
-                from rosbags.typesys.stores.latest import (
+                from rosbags.typesys.stores.latest import (  # type: ignore
                     sensor_msgs__msg__PointCloud2 as PointCloud2,
                 )
-                from rosbags.typesys.stores.latest import (
+                from rosbags.typesys.stores.latest import (  # type: ignore
                     sensor_msgs__msg__PointField as PointField,
                 )
-                from rosbags.typesys.stores.latest import (
+                from rosbags.typesys.stores.latest import (  # type: ignore
                     std_msgs__msg__Header as Header,
                 )
 
@@ -1037,12 +1037,11 @@ def __getitem__(
         )
         """
 
-        points_list: list[npt.NDArray]
         fields = self.fields
         types = self.types
         if isinstance(subscript, slice):
             points_list = tuple(
-                self.pc_data[field][subscript]
+                cast(npt.NDArray, self.pc_data[field][subscript])
                 for field in self.pc_data.dtype.names  # type: ignore[assignment,union-attr]
             )
         elif isinstance(subscript, np.ndarray):
@@ -1051,19 +1050,23 @@ def __getitem__(
                 raise ValueError(f"Mask array must be 1-dimensional but got {mask.ndim}")
 
             points_list = tuple(
-                self.pc_data[field][mask]
+                cast(npt.NDArray, self.pc_data[field][mask])
                 for field in self.pc_data.dtype.names  # type: ignore[assignment,union-attr]
             )
-        elif isinstance(subscript, str) or all(isinstance(s, str) for s in subscript):
+        elif isinstance(subscript, str) or all(isinstance(s, str) for s in cast(tuple, subscript)):
             if isinstance(subscript, str):
                 subscript = (subscript,)
 
+            subscript = cast(tuple, subscript)
+
             if not np.isin(subscript, self.fields).all():
                 raise ValueError(f"Invalid field name(s): {subscript}")
 
-            points_list = [self.pc_data[field] for field in subscript]
+            points_list = tuple(cast(npt.NDArray, self.pc_data[field]) for field in subscript)
             fields = tuple(subscript)
             types = tuple(self.pc_data[field].dtype for field in subscript)
+        else:
+            raise ValueError(f"Invalid subscript type: {type(subscript).__name__}")
 
         return PointCloud.from_points(points_list, fields, types)