diff --git a/Lib/distutils/command/build_ext.py b/Lib/distutils/command/build_ext.py
index 2d7cdf063f01db..38bb8fd93c2781 100644
--- a/Lib/distutils/command/build_ext.py
+++ b/Lib/distutils/command/build_ext.py
@@ -490,7 +490,8 @@ def build_extension(self, ext):
                   "in 'ext_modules' option (extension '%s'), "
                   "'sources' must be present and must be "
                   "a list of source filenames" % ext.name)
-        sources = list(sources)
+        # sort to make the resulting .so file build reproducible
+        sources = sorted(sources)
 
         ext_path = self.get_ext_fullpath(ext.name)
         depends = sources + ext.depends
diff --git a/Misc/NEWS.d/next/Library/2019-03-21-19-23-46.bpo-36302.Yc591g.rst b/Misc/NEWS.d/next/Library/2019-03-21-19-23-46.bpo-36302.Yc591g.rst
new file mode 100644
index 00000000000000..fe01b5915d5db7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-03-21-19-23-46.bpo-36302.Yc591g.rst
@@ -0,0 +1,2 @@
+distutils sorts source file lists so that Extension .so files
+build more reproducibly by default