diff --git a/setup.py b/setup.py
index c67fa02..51ab47d 100644
--- a/setup.py
+++ b/setup.py
@@ -16,6 +16,7 @@
         'include/pybind11/detail/common.h',
         'include/pybind11/detail/descr.h',
         'include/pybind11/detail/init.h',
+        'include/pybind11/detail/internals.h',
         'include/pybind11/detail/typeid.h'
         'include/pybind11/attr.h',
         'include/pybind11/buffer_info.h',