Index: library/nx/nx.tcl
===================================================================
diff -u -N -r3ccbf1417d84765af57693523035ecf857e37428 -r6280104bd82ee1e4f3c6bd824d1cc6d0482f43c0
--- library/nx/nx.tcl	(.../nx.tcl)	(revision 3ccbf1417d84765af57693523035ecf857e37428)
+++ library/nx/nx.tcl	(.../nx.tcl)	(revision 6280104bd82ee1e4f3c6bd824d1cc6d0482f43c0)
@@ -1061,6 +1061,9 @@
         lappend noptions $type
       }
     }
+    if {[dict exists $options -arg]} {
+      lappend noptions arg=[dict get $options -arg]
+    }
     if {[dict exists $options -multiplicity]} {
       lappend noptions [dict get $options -multiplicity]
     }