Use sequence repetition instead of bytes constructor with integer argument.
diff --git a/Lib/base64.py b/Lib/base64.py
index 67e54f0..58f6ad6 100755
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -155,7 +155,7 @@
     leftover = len(s) % 5
     # Pad the last quantum with zero bits if necessary
     if leftover:
-        s = s + bytes(5 - leftover)  # Don't use += !
+        s = s + b'\0' * (5 - leftover)  # Don't use += !
     encoded = bytearray()
     from_bytes = int.from_bytes
     b32tab2 = _b32tab2