diff --git a/doc/generic/pgf/text-en/pgfmanual-en-base-transparency.tex b/doc/generic/pgf/text-en/pgfmanual-en-base-transparency.tex
index fda8f6a88..22156f98d 100644
--- a/doc/generic/pgf/text-en/pgfmanual-en-base-transparency.tex
+++ b/doc/generic/pgf/text-en/pgfmanual-en-base-transparency.tex
@@ -349,6 +349,7 @@ \subsection{Transparency Groups}
     is ``large enough'' and then insert this picture into the main picture
     while ignoring the size. The following example shows how this is done:
 
+% TODO: Nesting tikzpictures is NOT supported
 {\tikzexternaldisable
 \begin{codeexample}[]
 \begin{tikzpicture}