diff --git a/lib/rb/Makefile.am b/lib/rb/Makefile.am
index 9cfffc7..da45ed5 100644
--- a/lib/rb/Makefile.am
+++ b/lib/rb/Makefile.am
@@ -29,7 +29,7 @@
 	spec
 
 all-local:
-	$(RUBY) setup.rb config
+	if [ -n "$(RUBY_PREFIX)" ] ; then $(RUBY) setup.rb config --prefix=$(DESTDIR)$(RUBY_PREFIX) --rbdir='$$libdir/ruby' --sodir='$$libdir/ruby' ; elif [ -n "$(DESTDIR)" ] ; then $(RUBY) setup.rb config --prefix=$(DESTDIR) ; else $(RUBY) setup.rb config ; fi
 	$(RUBY) setup.rb setup
 
 install-exec-hook: