diff --git a/acceptance/bin/update_file.py b/acceptance/bin/update_file.py
index ef643239533..8a69d5f5fef 100755
--- a/acceptance/bin/update_file.py
+++ b/acceptance/bin/update_file.py
@@ -5,6 +5,10 @@
 Replace all strings OLD with NEW in FILENAME.
 
 If OLD is not found in FILENAME, the script reports error.
+
+The file is read and written as bytes so that only the matched bytes change.
+Text mode on Windows rewrites every line ending as CRLF, which changes the
+file's content hash and upload payload.
 """
 
 import sys
@@ -20,9 +24,19 @@
 # call update_file.py on that file.
 assert filename != "output.txt"
 
-data = open(filename).read()
-newdata = data.replace(old, new)
+with open(filename, "rb") as fobj:
+    data = fobj.read()
+
+old_bytes = old.encode()
+new_bytes = new.encode()
+
+# Match the file's line endings so multi-line OLD/NEW work on CRLF checkouts.
+if b"\r\n" in data:
+    old_bytes = old_bytes.replace(b"\r\n", b"\n").replace(b"\n", b"\r\n")
+    new_bytes = new_bytes.replace(b"\r\n", b"\n").replace(b"\n", b"\r\n")
+
+newdata = data.replace(old_bytes, new_bytes)
 if newdata == data:
-    sys.exit(f"{old=} not found in {filename=}\n{data}")
-with open(filename, "w") as fobj:
+    sys.exit(f"{old=} not found in {filename=}\n{data.decode(errors='replace')}")
+with open(filename, "wb") as fobj:
     fobj.write(newdata)