diff --git a/ChangeLog b/ChangeLog
index 67b207ce..c72253ab 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2009-02-05  Eric Blake  <ebb9@byu.net>
+
+	Mention new AC_DEFUN_ONCE clients.
+	* NEWS: Mention recent semantic changes.
+	Reported by Ralf Wildenhues.
+
 2009-02-03  Eric Blake  <ebb9@byu.net>
 
 	Use AC_DEFUN_ONCE for some one-shot AC_PROG macros.
diff --git a/NEWS b/NEWS
index ba006cd8..94b310e3 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,16 @@ GNU Autoconf NEWS - User visible changes.
    and subsequent invocations are a silent no-op.  This makes
    AC_DEFUN_ONCE an ideal macro for silencing AC_REQUIRE warnings.
 
+** The following macros are now defined with AC_DEFUN_ONCE.  This means
+   a subtle change in semantics; previously, an AC_DEFUN macro could
+   expand one of these macros multiple times or surround the macro
+   inside shell conditional text to bypass the effects of these
+   macros, but now the macro will expand exactly once, and prior to
+   the start of any enclosing AC_DEFUN macro:
+   AC_CANONICAL_BUILD  AC_CANONICAL_HOST  AC_CANONICAL_TARGET
+   AC_HEADER_ASSERT  AC_PROG_INSTALL  AC_PROG_MKDIR_P
+   AC_USE_SYSTEM_EXTENSIONS
+
 ** AC_LANG_ERLANG works once again (regression introduced in 2.61a).
 
 ** AC_HEADER_ASSERT is fixed so that './configure --enable-assert' no