diff --git a/doc/Makefile.am b/doc/Makefile.am
index c998e63..ed3a6d5 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -67,5 +67,5 @@
 	mpls/opaque_lsa.txt mpls/ospfd.conf \
 	$(figures_sources) $(figures_png) $(figures_txt)
 
-draft-zebra-00.txt:
-	groff -T ascii -ms draft-zebra-00.ms > draft-zebra-00.txt
+draft-zebra-00.txt: draft-zebra-00.ms
+	groff -T ascii -ms $< > $@