diff --git a/lib/rb/Makefile.am b/lib/rb/Makefile.am
index 43acfff..07fc5c6 100644
--- a/lib/rb/Makefile.am
+++ b/lib/rb/Makefile.am
@@ -7,7 +7,9 @@
 install-exec-hook:
 	$(RUBY) setup.rb install
 
+# Make sure this doesn't fail if Ruby is not configured.
 clean-local:
-	$(RUBY) setup.rb clean
+	RUBY=$(RUBY) ; if test -z "$$RUBY" ; then RUBY=: ; fi ; \
+	$$RUBY setup.rb clean
 
 check-local: all