diff --git a/megatron/data/indexed_dataset.py b/megatron/data/indexed_dataset.py
index 2b2c1f405..acdf36246 100644
--- a/megatron/data/indexed_dataset.py
+++ b/megatron/data/indexed_dataset.py
@@ -359,22 +359,16 @@ def _get_pointers(sizes, npdtype):
                     """Return a numpy array of byte offsets given a list of sizes.
 
                     Multiplies values in the sizes array by dtype size (bytes),
-                    and then computes a zero-based prefix scan.
+                    and then computes an exclusive scan to get byte offsets.
                     """
 
-                    # create numpy array of desired numpy datatype
-                    pointers = np.array(sizes, dtype=npdtype)
+                    # compute element sizes in bytes
+                    bytesizes = np.array(sizes, dtype=npdtype)
+                    bytesizes *= dtype().itemsize
 
-                    if len(sizes) > 0:
-                        # scale each element by its dtype size
-                        dtype_size = dtype().itemsize
-                        pointers *= dtype_size
-
-                        # in-place prefix scan to compute byte offsets
-                        np.cumsum(pointers, axis=0, out=pointers)
-
-                        # zero-base the prefix scan (exclusive scan)
-                        pointers -= pointers[0]
+                    # exclusive scan to get byte offsets
+                    pointers = np.cumsum(bytesizes, axis=0)
+                    pointers -= bytesizes
 
                     return pointers