diff --git a/scico/numpy/util.py b/scico/numpy/util.py
index 54a1c497d..a31a7fe4b 100644
--- a/scico/numpy/util.py
+++ b/scico/numpy/util.py
@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Copyright (C) 2022-2023 by SCICO Developers
+# Copyright (C) 2022-2024 by SCICO Developers
 # All rights reserved. BSD 3-clause License.
 # This file is part of the SPORCO package. Details of the copyright
 # and user license can be found in the 'LICENSE.txt' file distributed
@@ -87,7 +87,8 @@ def slice_length(length: int, idx: AxisIndex) -> Optional[int]:
 
     Raises:
         ValueError: If `idx` is an integer index that is out bounds for
-            the axis length.
+            the axis length or if the type of `idx` is not one of
+            `Ellipsis`, `int`, or `slice`.
     """
     if idx is Ellipsis:
         return length
@@ -95,6 +96,8 @@ def slice_length(length: int, idx: AxisIndex) -> Optional[int]:
         if idx < -length or idx > length - 1:
             raise ValueError(f"Index {idx} out of bounds for axis of length {length}.")
         return None
+    if not isinstance(idx, slice):
+        raise ValueError(f"Index expression {idx} is of an unrecognized type.")
     start, stop, stride = idx.indices(length)
     if start > stop:
         start = stop
@@ -112,19 +115,24 @@ def indexed_shape(shape: Shape, idx: ArrayIndex) -> Tuple[int, ...]:
         Shape of indexed/sliced array.
 
     Raises:
-        ValueError: If `idx` is longer than `shape`.
+        ValueError: If any element of `idx` is not one of `Ellipsis`,
+        `int`, `slice`, or ``None`` (`np.newaxis`), or if an integer
+        index is out bounds for the corresponding axis length.
     """
     if not isinstance(idx, tuple):
         idx = (idx,)
-    if len(idx) > len(shape):
-        raise ValueError(f"Slice {idx} has more dimensions than shape {shape}.")
     idx_shape: List[Optional[int]] = list(shape)
     offset = 0
+    newaxis = 0
     for axis, ax_idx in enumerate(idx):
+        if ax_idx is None:
+            idx_shape.insert(axis, 1)
+            newaxis += 1
+            continue
         if ax_idx is Ellipsis:
             offset = len(shape) - len(idx)
             continue
-        idx_shape[axis + offset] = slice_length(shape[axis + offset], ax_idx)
+        idx_shape[axis + offset + newaxis] = slice_length(shape[axis + offset], ax_idx)
     return tuple(filter(lambda x: x is not None, idx_shape))  # type: ignore
 
 
diff --git a/scico/test/linop/test_func.py b/scico/test/linop/test_func.py
index 2376ca2f5..a6741ba47 100644
--- a/scico/test/linop/test_func.py
+++ b/scico/test/linop/test_func.py
@@ -91,6 +91,8 @@ def slicetestobj(request):
     np.s_[1:, :-3],
     np.s_[1:, :, :3],
     np.s_[1:, ..., 2:],
+    np.s_[np.newaxis],
+    np.s_[:, np.newaxis],
 ]
 
 
diff --git a/scico/test/numpy/test_numpy_util.py b/scico/test/numpy/test_numpy_util.py
index faab01dc5..c781b56e1 100644
--- a/scico/test/numpy/test_numpy_util.py
+++ b/scico/test/numpy/test_numpy_util.py
@@ -99,6 +99,10 @@ def test_slice_length_other(length, slc):
         np.s_[..., 2:],
         np.s_[..., 2:, :],
         np.s_[1:, ..., 2:],
+        np.s_[np.newaxis],
+        np.s_[:, np.newaxis],
+        np.s_[np.newaxis, :, np.newaxis],
+        np.s_[np.newaxis, ..., 0:2, :],
     ),
 )
 def test_indexed_shape(shape, slc):