diff --git a/lib/metanorma/ietf/processor.rb b/lib/metanorma/ietf/processor.rb
index a7f4993..02fc0ea 100644
--- a/lib/metanorma/ietf/processor.rb
+++ b/lib/metanorma/ietf/processor.rb
@@ -83,7 +83,7 @@ def xml2rfc(isodoc_node, inname, outname, format, options)
         outflag = { txt: "--text", pdf: "--pdf", html: "--html" }[format]
 
         outname ||= inname.sub(/\.xml$/, outext)
-        system("xml2rfc #{outflag} #{rfcname} -o #{outname}")
+        system("xml2rfc", outflag, rfcname, "-o", outname)
       end
     end
   end