diff --git a/CMakeLists.txt b/CMakeLists.txt
index a423ae442..38443da66 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -115,6 +115,7 @@ set(PYBIND11_HEADERS
     include/pybind11/detail/smart_holder_sfinae_hooks_only.h
     include/pybind11/detail/smart_holder_type_casters.h
     include/pybind11/detail/type_caster_base.h
+    include/pybind11/detail/type_caster_odr_guard.h
     include/pybind11/detail/typeid.h
     include/pybind11/attr.h
     include/pybind11/buffer_info.h
diff --git a/tests/extra_python_package/test_files.py b/tests/extra_python_package/test_files.py
index 8206000c9..7bcb5e59d 100644
--- a/tests/extra_python_package/test_files.py
+++ b/tests/extra_python_package/test_files.py
@@ -48,6 +48,7 @@ detail_headers = {
     "include/pybind11/detail/smart_holder_sfinae_hooks_only.h",
     "include/pybind11/detail/smart_holder_type_casters.h",
     "include/pybind11/detail/type_caster_base.h",
+    "include/pybind11/detail/type_caster_odr_guard.h",
     "include/pybind11/detail/typeid.h",
 }