diff --git a/distributed/protocol/utils.py b/distributed/protocol/utils.py
index 66c9687bae..d5694a1b3f 100644
--- a/distributed/protocol/utils.py
+++ b/distributed/protocol/utils.py
@@ -23,21 +23,15 @@ def frame_split_size(frame, n=BIG_BYTES_SHARD_SIZE) -> list:
     >>> frame_split_size([b'12345', b'678'], n=3)  # doctest: +SKIP
     [b'123', b'45', b'678']
     """
-    if nbytes(frame) <= n:
+    frame = memoryview(frame)
+
+    if frame.nbytes <= n:
         return [frame]
 
-    if nbytes(frame) > n:
-        if isinstance(frame, (bytes, bytearray)):
-            frame = memoryview(frame)
-        try:
-            itemsize = frame.itemsize
-        except AttributeError:
-            itemsize = 1
+    nitems = frame.nbytes // frame.itemsize
+    items_per_shard = n // frame.itemsize
 
-        return [
-            frame[i : i + n // itemsize]
-            for i in range(0, nbytes(frame) // itemsize, n // itemsize)
-        ]
+    return [frame[i : i + items_per_shard] for i in range(0, nitems, items_per_shard)]
 
 
 def merge_frames(header, frames):