diff --git a/klamath/basic.py b/klamath/basic.py
index 6d4d924..95f5551 100644
--- a/klamath/basic.py
+++ b/klamath/basic.py
@@ -1,7 +1,8 @@
 """
 Functionality for encoding/decoding basic datatypes
 """
-from typing import Sequence, IO
+from typing import IO
+from collections.abc import Sequence
 import struct
 import logging
 from datetime import datetime
diff --git a/klamath/elements.py b/klamath/elements.py
index a1a10d7..302921c 100644
--- a/klamath/elements.py
+++ b/klamath/elements.py
@@ -2,7 +2,7 @@
 Functionality for reading/writing elements (geometry, text labels,
  structure references) and associated properties.
 """
-from typing import Optional, IO, TypeVar, Type, Union
+from typing import IO, TypeVar
 from abc import ABCMeta, abstractmethod
 from dataclasses import dataclass
 
@@ -78,7 +78,7 @@ class Element(metaclass=ABCMeta):
     """
     @classmethod
     @abstractmethod
-    def read(cls: Type[E], stream: IO[bytes]) -> E:
+    def read(cls: type[E], stream: IO[bytes]) -> E:
         """
         Read from a stream to construct this object.
         Consumes up to (and including) the ENDEL record.
@@ -151,7 +151,7 @@ class Reference(Element):
     """ Properties associated with this reference. """
 
     @classmethod
-    def read(cls: Type[R], stream: IO[bytes]) -> R:
+    def read(cls: type[R], stream: IO[bytes]) -> R:
         invert_y = False
         mag = 1
         angle_deg = 0
@@ -233,7 +233,7 @@ class Boundary(Element):
     """ Properties for the element. """
 
     @classmethod
-    def read(cls: Type[B], stream: IO[bytes]) -> B:
+    def read(cls: type[B], stream: IO[bytes]) -> B:
         layer = LAYER.skip_and_read(stream)[0]
         dtype = DATATYPE.read(stream)[0]
         xy = XY.read(stream).reshape(-1, 2)
@@ -279,7 +279,7 @@ class Path(Element):
     """ Properties for the element. """
 
     @classmethod
-    def read(cls: Type[P], stream: IO[bytes]) -> P:
+    def read(cls: type[P], stream: IO[bytes]) -> P:
         path_type = 0
         width = 0
         bgn_ext = 0
@@ -344,7 +344,7 @@ class Box(Element):
     """ Properties for the element. """
 
     @classmethod
-    def read(cls: Type[X], stream: IO[bytes]) -> X:
+    def read(cls: type[X], stream: IO[bytes]) -> X:
         layer = LAYER.skip_and_read(stream)[0]
         dtype = BOXTYPE.read(stream)[0]
         xy = XY.read(stream).reshape(-1, 2)
@@ -378,7 +378,7 @@ class Node(Element):
     """ Properties for the element. """
 
     @classmethod
-    def read(cls: Type[N], stream: IO[bytes]) -> N:
+    def read(cls: type[N], stream: IO[bytes]) -> N:
         layer = LAYER.skip_and_read(stream)[0]
         dtype = NODETYPE.read(stream)[0]
         xy = XY.read(stream).reshape(-1, 2)
@@ -438,7 +438,7 @@ class Text(Element):
     """ Properties for the element. """
 
     @classmethod
-    def read(cls: Type[T], stream: IO[bytes]) -> T:
+    def read(cls: type[T], stream: IO[bytes]) -> T:
         path_type = 0
         presentation = 0
         invert_y = False
diff --git a/klamath/library.py b/klamath/library.py
index 239609d..4021677 100644
--- a/klamath/library.py
+++ b/klamath/library.py
@@ -1,7 +1,7 @@
 """
 File-level read/write functionality.
 """
-from typing import IO, TypeVar, Type, MutableMapping
+from typing import IO, Self, TYPE_CHECKING
 import io
 from datetime import datetime
 from dataclasses import dataclass
@@ -15,8 +15,8 @@ from .records import BGNSTR, STRNAME, ENDSTR, SNAME, COLROW, ENDEL
 from .records import BOX, BOUNDARY, NODE, PATH, TEXT, SREF, AREF
 from .elements import Element, Reference, Text, Box, Boundary, Path, Node
 
-
-FH = TypeVar('FH', bound='FileHeader')
+if TYPE_CHECKING:
+    from collections.abc import MutableMapping
 
 
 @dataclass
@@ -45,7 +45,7 @@ class FileHeader:
     """ Last-accessed time """
 
     @classmethod
-    def read(cls: Type[FH], stream: IO[bytes]) -> FH:
+    def read(cls: type[Self], stream: IO[bytes]) -> Self:
         """
         Read and construct a header from the provided stream.
 
diff --git a/klamath/records.py b/klamath/records.py
index 9fe296d..31db805 100644
--- a/klamath/records.py
+++ b/klamath/records.py
@@ -1,7 +1,10 @@
 """
 Record type and tag definitions
 """
-from typing import Sequence
+from typing import Self
+from collections.abc import Sequence, Sized
+import numpy
+from numpy.typing import NDArray
 
 from .record import NoDataRecord, BitArrayRecord, Int2Record, Int4Record, Real8Record
 from .record import ASCIIRecord, DateTimeRecord
@@ -169,7 +172,7 @@ class GENERATIONS(Int2Record):
 
     @classmethod
     def check_data(cls: type[Self], data: NDArray[numpy.integer] | Sequence[int] | int) -> None:
-        if len(data) != 1:
+        if not isinstance(data, Sized) or len(data) != 1:
             raise Exception(f'Expected exactly one integer, got {data}')
 
 
@@ -267,7 +270,7 @@ class FORMAT(Int2Record):
 
     @classmethod
     def check_data(cls: type[Self], data: NDArray[numpy.integer] | Sequence[int] | int) -> None:
-        if len(data) != 1:
+        if not isinstance(data, Sized) or len(data) != 1:
             raise Exception(f'Expected exactly one integer, got {data}')