diff --git a/reference/reflection/book.xml b/reference/reflection/book.xml
index 9fb3002b53..9231a730c2 100644
--- a/reference/reflection/book.xml
+++ b/reference/reflection/book.xml
@@ -13,6 +13,13 @@
    methods and extensions. Additionally, the reflection API offers ways to
    retrieve doc comments for functions, classes and methods.
   </para>
+  <para>
+   Please note that certain parts of the internal <acronym>API</acronym>
+   are missing the necessary code to work with the Reflection extension.
+   E.g., an internal PHP class might be missing reflection data for
+   properties. These few cases are considered bugs, however, so they
+   should be discovered and fixed.
+  </para>
  </preface>
 
  &reference.reflection.setup;