diff --git a/CHANGES.rst b/CHANGES.rst
index 17c1a19..070ce38 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,6 +5,8 @@ Unreleased
 
 -   Drop support for Python 3.8 and 3.9.
 -   Remove previously deprecated code.
+-   Fix raising ``BadData`` on payload without padding on Python 3.15.
+    :issue:`420`
 
 
 Version 2.2.0
diff --git a/src/itsdangerous/encoding.py b/src/itsdangerous/encoding.py
index f5ca80f..1136d3e 100644
--- a/src/itsdangerous/encoding.py
+++ b/src/itsdangerous/encoding.py
@@ -3,6 +3,7 @@
 import base64
 import string
 import struct
+import sys
 import typing as t
 
 from .exc import BadData
@@ -33,7 +34,10 @@ def base64_decode(string: str | bytes) -> bytes:
     string += b"=" * (-len(string) % 4)
 
     try:
-        return base64.urlsafe_b64decode(string)
+        if sys.version_info >= (3, 15):
+            return base64.urlsafe_b64decode(string, padded=True)
+        else:
+            return base64.urlsafe_b64decode(string)
     except (TypeError, ValueError) as e:
         raise BadData("Invalid base64-encoded data") from e