diff --git a/src/highdicom/color.py b/src/highdicom/color.py
index 4725677d..8a52dc81 100644
--- a/src/highdicom/color.py
+++ b/src/highdicom/color.py
@@ -17,7 +17,7 @@
 logger = logging.getLogger(__name__)
 
 
-class CIELabColor(object):
+class CIELabColor:
 
     """Class to represent a color value in CIELab color space."""
 
@@ -67,7 +67,7 @@ def value(self) -> Tuple[int, int, int]:
         return self._value
 
 
-class ColorManager(object):
+class ColorManager:
 
     """Class for color management using ICC profiles."""
 
diff --git a/src/highdicom/io.py b/src/highdicom/io.py
index 5062b8e4..551c768e 100644
--- a/src/highdicom/io.py
+++ b/src/highdicom/io.py
@@ -217,7 +217,7 @@ def _stop_after_group_2(tag: pydicom.tag.BaseTag, vr: str, length: int) -> bool:
     return tag.group > 2
 
 
-class ImageFileReader(object):
+class ImageFileReader:
 
     """Reader for DICOM datasets representing Image Information Entities.
 
diff --git a/src/highdicom/spatial.py b/src/highdicom/spatial.py
index f317f2c9..54a64925 100644
--- a/src/highdicom/spatial.py
+++ b/src/highdicom/spatial.py
@@ -198,7 +198,7 @@ def _create_inv_affine_transformation_matrix(
     )
 
 
-class PixelToReferenceTransformer(object):
+class PixelToReferenceTransformer:
 
     """Class for transforming pixel indices to reference coordinates.
 
@@ -338,7 +338,7 @@ def __call__(self, indices: np.ndarray) -> np.ndarray:
         return reference_coordinates[:3, :].T
 
 
-class ReferenceToPixelTransformer(object):
+class ReferenceToPixelTransformer:
 
     """Class for transforming reference coordinates to pixel indices.
 
@@ -481,7 +481,7 @@ def __call__(self, coordinates: np.ndarray) -> np.ndarray:
         return np.around(pixel_matrix_coordinates[:3, :].T).astype(int)
 
 
-class ImageToReferenceTransformer(object):
+class ImageToReferenceTransformer:
 
     """Class for transforming coordinates from image to reference space.
 
@@ -619,7 +619,7 @@ def __call__(self, coordinates: np.ndarray) -> np.ndarray:
         return reference_coordinates[:3, :].T
 
 
-class ReferenceToImageTransformer(object):
+class ReferenceToImageTransformer:
 
     """Class for transforming coordinates from reference to image space.