diff --git a/Doc/ext/extending.tex b/Doc/ext/extending.tex
index 95e4546..c50714e 100644
--- a/Doc/ext/extending.tex
+++ b/Doc/ext/extending.tex
@@ -46,9 +46,12 @@
 
 which pulls in the Python API (you can add a comment describing the
 purpose of the module and a copyright notice if you like).
-Since Python may define some pre-processor definitions which affect
-the standard headers on some systems, you must include \file{Python.h}
-before any standard headers are included.
+
+\begin{notice}[warning]
+  Since Python may define some pre-processor definitions which affect
+  the standard headers on some systems, you \emph{must} include
+  \file{Python.h} before any standard headers are included.
+\end{notice}
 
 All user-visible symbols defined by \file{Python.h} have a prefix of
 \samp{Py} or \samp{PY}, except those defined in standard header files.