diff --git a/mercurial/archival.py b/mercurial/archival.py
--- a/mercurial/archival.py
+++ b/mercurial/archival.py
@@ -218,7 +218,7 @@
                 dest.tell()
             except (AttributeError, IOError):
                 dest = tellable(dest)
-        self.z = zipfile.ZipFile(dest, 'w',
+        self.z = zipfile.ZipFile(dest, r'w',
                                  compress and zipfile.ZIP_DEFLATED or
                                  zipfile.ZIP_STORED)