diff -up ghostscript-8.63/src/iname.c.465311 ghostscript-8.63/src/iname.c
--- ghostscript-8.63/src/iname.c.465311	2008-10-17 11:52:31.000000000 +0100
+++ ghostscript-8.63/src/iname.c	2008-10-17 11:53:08.000000000 +0100
@@ -415,7 +415,8 @@ names_trace_finish(name_table * nt, gc_s
 	    if (nt->sub[i].names == 0 && gcst != 0) {
 		/* Mark the just-freed sub-table as unmarked. */
 		o_set_unmarked((obj_header_t *)sub - 1);
-		o_set_unmarked((obj_header_t *)ssub - 1);
+		if (ssub != 0)
+		    o_set_unmarked((obj_header_t *)ssub - 1);
 	    }
 	}
 	if (i == 0)