diff --git a/win/tools/1337-diff/1337-diff.py b/win/tools/1337-diff/1337-diff.py
index c9ab947..a1c196d 100755
--- a/win/tools/1337-diff/1337-diff.py
+++ b/win/tools/1337-diff/1337-diff.py
@@ -64,24 +64,29 @@ def feed_chunks(f, chunk_size=4096):
         yield buf
 
 
-def zip_files_bytes(*files):
+def zip_files_bytes(left, right):
     """ Iterate over two files, returning pair of bytes.
     Throw LengthMismatch if file sizes is uneven. """
     class EndMarker(object):
         pass
     end_marker = EndMarker()
 
-    iterators = (itertools.chain.from_iterable(feed_chunks(f)) for f in files)
-    for tup in itertools.zip_longest(*iterators, fillvalue=end_marker):
-        if any(v is end_marker for v in tup):
+    left_iter = itertools.chain.from_iterable(feed_chunks(left))
+    right_iter = itertools.chain.from_iterable(feed_chunks(right))
+    for a, b in itertools.zip_longest(left_iter,
+                                      right_iter,
+                                      fillvalue=end_marker):
+        if a is end_marker or b is end_marker:
             raise LengthMismatchException("Length of input files inequal.")
-        yield tup
+        yield a, b
 
 
 def diff(left, right):
-    for offset, (a, b) in enumerate(zip_files_bytes(left, right)):
+    offset = 0
+    for a, b in zip_files_bytes(left, right):
         if a != b:
             yield offset, a, b
+        offset += 1
 
 
 def compose_diff_file(orig, patched, output, header, offset_adjustment=True):