diff --git a/doc/misc/cc-mode.texi b/doc/misc/cc-mode.texi
index 8ac9588c30599d18b4995271689d98a8ad55e935..0bbe639e6db1d47ffdfa3281fd3994055ca6ec26 100644
--- a/doc/misc/cc-mode.texi
+++ b/doc/misc/cc-mode.texi
@@ -6759,6 +6759,14 @@ it and font-locks it OK.  Templates used in expressions, and nested
 templates do not fare so well.  Sometimes a workaround is to refontify
 the expression after typing the closing @samp{>}.
 
+@item
+In a @dfn{k&r region} (the part of an old-fashioned C function
+declaration which specifies the types of its parameters, coming
+between the parameter list and the opening brace), there should be at
+most 20 top-level parenthesis and bracket pairs.  This limit has been
+imposed for performance reasons.  If it is violated, the source file
+might be incorrectly indented or fontified.
+
 @item
 On loading @ccmode{}, sometimes this error message appears:
 
diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index d162ea33fb1aa533e23c4487cf3f726a546fcd16..9d267a7d863010324067d802e84226bd4559abe2 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2008-03-07  Alan Mackenzie  <acm@muc.de>
+
+	* progmodes/cc-engine.el (c-in-knr-argdecl): Limit number of
+	paren/bracket pairs parsed, to solve performance problem.
+
 2008-03-07  Bastien Guerry  <bzg@altern.org>
 
 	* bookmark.el (bookmark-set): Don't check for