diff --git a/docs/reference/internal_modules.rst b/docs/reference/internal_modules.rst
index 41a8837b30a..1b43d1a35cb 100644
--- a/docs/reference/internal_modules.rst
+++ b/docs/reference/internal_modules.rst
@@ -82,6 +82,9 @@ on some Python versions.
 An internal interface module previously known as :mod:`~PIL._imaging`,
 implemented in :file:`_imaging.c`.
 
+Pillow is a Python library, and the C interfaces within are for internal use only.
+They may change without a deprecation period or a mention in the release notes.
+
 .. py:class:: ImagingCore
 
     A representation of the image data.