1 files changed, 3 insertions, 0 deletions
diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index c8931687a3c..8cb5279d735 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -300,6 +300,9 @@ class PurePath(os.PathLike):
         for arg in args:
             if isinstance(arg, PurePath):
                 path = arg._raw_path
+                if arg._flavour is ntpath and self._flavour is posixpath:
+                    # GH-103631: Convert separators for backwards compatibility.
+                    path = path.replace('\\', '/')
             else:
                 try:
                     path = os.fspath(arg)