diff --git a/setup.py b/setup.py
index ce9df3a99ab..a0066083a3c 100644
--- a/setup.py
+++ b/setup.py
@@ -424,7 +424,7 @@ class build_ext(build_ext_parent):
                         os.remove(cfile)
                     shutil.copyfile(hfile, cfile)
 
-                C.main_sources += cfile_list
+                C.sources += cfile_list
         if WITH_NINJA:
             # before we start the normal build make sure all generated code
             # gets built