diff --git a/Doc/glossary.rst b/Doc/glossary.rst
index 705b0a9279c6d4..199a917f9f101e 100644
--- a/Doc/glossary.rst
+++ b/Doc/glossary.rst
@@ -1208,6 +1208,11 @@ Glossary
       :func:`sys.getrefcount` function to return the
       reference count for a particular object.
 
+      In :term:`CPython`, reference counts are not considered to be stable
+      or well-defined values; the number of references to an object, and how
+      that number is affected by Python code, may be different between
+      versions.
+
    regular package
       A traditional :term:`package`, such as a directory containing an
       ``__init__.py`` file.