diff --git a/ox/net.py b/ox/net.py
index 200a2b4..3d4c52e 100644
--- a/ox/net.py
+++ b/ox/net.py
@@ -145,8 +145,9 @@ def oshash(url):
         if filesize > 65536:
             tail = get_range(url, filesize-65536, filesize)
         if filesize < 65536:
-            for offset in range(0, filesize, bytesize):
-                buffer = head[offset:offset+bytesize]
+            f = BytesIO(head)
+            for x in range(int(filesize/bytesize)):
+                buffer = f.read(bytesize)
                 (l_value,)= struct.unpack(longlongformat, buffer)
                 hash += l_value
                 hash = hash & 0xFFFFFFFFFFFFFFFF #cut off 64bit overflow