http://bugs.gentoo.org/189671
http://lists.gnu.org/archive/html/bug-bash/2007-08/msg00081.html

--- bash-3.2/Makefile.in
+++ bash-3.2/Makefile.in
@@ -584,7 +584,9 @@
 	@( { test "${RL_LIBDIR}" = "${libdir}" && exit 0; } || \
 		cd ${RL_LIBDIR} && $(MAKE) $(MFLAGS) libreadline.a) || exit 1
 
-$(HISTORY_LIBRARY): config.h $(HISTORY_SOURCE)
+# prevent parallel build race conditions in the lib/readline/ subdir
+# by depending on libreadline.a when applicable
+$(HISTORY_LIBRARY): config.h $(HISTORY_SOURCE) $(READLINE_DEP)
 	@echo making $@ in ${HIST_LIBDIR}
 	@( { test "${HIST_LIBDIR}" = "${libdir}" && exit 0; } || \
 		cd ${HIST_LIBDIR} && $(MAKE) $(MFLAGS) libhistory.a) || exit 1