--- a/lisp/ChangeLog	Fri Sep 09 22:50:31 2011 +0100
+++ b/lisp/ChangeLog	Sat Sep 10 13:17:29 2011 +0100
@@ -1,3 +1,13 @@
+2011-09-10  Aidan Kehoe  <kehoea@parhasard.net>
+
+	* cl-macs.el (cl-defsubst-expand):
+	Change set 2a6a8da4dd7c of
+	http://mid.gmane.org/19966.17522.332164.615228@parhasard.net
+	wasn't sufficiently comprehensive, symbol macros can be mutually
+	rather than simply recursive, and they can equally hang. Thanks
+	for the bug report, Michael Sperber, and for the test case,
+	Stephen Turnbull.
+
 2011-09-09  Aidan Kehoe  <kehoea@parhasard.net>
 
 	* bytecomp.el (byte-compile-from-buffer):

--- a/lisp/cl-macs.el	Fri Sep 09 22:50:31 2011 +0100
+++ b/lisp/cl-macs.el	Sat Sep 10 13:17:29 2011 +0100
@@ -3236,10 +3236,20 @@
     (let* ((symbol-macros nil)
            (lets (mapcan #'(lambda (argn argv)
                              (if (or simple (cl-const-expr-p argv))
-                                 (progn (or (eq argn argv)
-					    (push (list argn argv)
-						  symbol-macros))
-                                        (and unsafe (list (list argn argv))))
+                                 (progn 
+				   ;; Avoid infinite loop on symbol macro
+				   ;; expansion, make sure none of the argvs
+				   ;; refer to the symbols in the argns.
+				   (or (block find
+                                         ;; Can't use cl-expr-contains, that
+                                         ;; doesn't descend lambdas:
+					 (subst nil argn argvs :test
+						#'(lambda (elt tree)
+						    (if (eq elt tree)
+							(return-from find t))))
+					 nil)
+				       (push (list argn argv) symbol-macros))
+				   (and unsafe (list (list argn argv))))
                                (list (list argn argv))))
                          argns argvs)))
       `(let ,lets