diff --git a/changelog.d/1424.change.rst b/changelog.d/1424.change.rst
new file mode 100644
index 0000000000..361997ddd6
--- /dev/null
+++ b/changelog.d/1424.change.rst
@@ -0,0 +1 @@
+Prevent keeping files mode for package_data build. It may break a build if user's package data has read only flag.
\ No newline at end of file
diff --git a/setuptools/command/build_py.py b/setuptools/command/build_py.py
index b0314fd413..6fc0a4e46d 100644
--- a/setuptools/command/build_py.py
+++ b/setuptools/command/build_py.py
@@ -120,7 +120,7 @@ def build_package_data(self):
                 target = os.path.join(build_dir, filename)
                 self.mkpath(os.path.dirname(target))
                 srcfile = os.path.join(src_dir, filename)
-                outf, copied = self.copy_file(srcfile, target)
+                outf, copied = self.copy_file(srcfile, target, preserve_mode=False)
                 srcfile = os.path.abspath(srcfile)
                 if (copied and
                         srcfile in self.distribution.convert_2to3_doctests):