--- a/src/Makefile.in	Thu Mar 09 19:21:39 2006 +0000
+++ b/src/Makefile.in	Fri Mar 10 03:57:23 2006 +0000
@@ -535,12 +535,21 @@
 __gnuplot_raw__.cc : DLD-FUNCTIONS/__gnuplot_raw__.l
 	$(LEX) $(LFLAGS) $< > $(@F)
 
-defaults.h: defaults.h.in ../Makeconf Makefile
+## We want to force an update of defaults.h and oct-conf.h every
+## time make is run because some values may come from the command
+## line or the environment.  The substitution rules use move-if-change,
+## so this should not cause trouble if the file already exists and the
+## newly generated file is not different.
+
+defaults.h: defaults.h.in ../Makeconf Makefile FORCE
 	@$(do-subst-default-vals)
 
-oct-conf.h: oct-conf.h.in ../Makeconf Makefile
+oct-conf.h: oct-conf.h.in ../Makeconf Makefile FORCE
 	@$(do-subst-config-vals)
 
+FORCE:
+.PHONY: FORCE
+
 oct-errno.cc: oct-errno.cc.in ../Makeconf Makefile
 	@echo "making $@ from $<"
 	@if test -n "$(PERL)"; then \