--- Makefile.pre.in
+++ Makefile.pre.in
@@ -983,7 +983,7 @@
 		multiprocessing multiprocessing/dummy \
 		unittest unittest/test \
 		curses pydoc_data $(MACHDEPS)
-libinstall:	build_all $(srcdir)/Lib/$(PLATDIR) $(srcdir)/Modules/xxmodule.c
+libinstall:	build_all updateplatdir $(srcdir)/Modules/xxmodule.c
 	@for i in $(SCRIPTDIR) $(LIBDEST); \
 	do \
 		if test ! -d $(DESTDIR)$$i; then \
@@ -1078,6 +1078,13 @@
 	export EXE; EXE="$(BUILDEXE)"; \
 	cd $(srcdir)/Lib/$(PLATDIR); $(RUNSHARED) ./regen
 
+updateplatdir: $(srcdir)/Lib/$(PLATDIR)
+	export PATH; PATH="`pwd`:$$PATH"; \
+	export PYTHONPATH; PYTHONPATH="`pwd`/Lib"; \
+	export DYLD_FRAMEWORK_PATH; DYLD_FRAMEWORK_PATH="`pwd`"; \
+	export EXE; EXE="$(BUILDEXE)"; \
+	cd $(srcdir)/Lib/$(PLATDIR); $(RUNSHARED) ./regen
+
 python-config: $(srcdir)/Misc/python-config.in
 	# Substitution happens here, as the completely-expanded BINDIR
 	# is not available in configure