diff --git a/elaborate.cc b/elaborate.cc
index c572f4ef8..e01a3f980 100644
--- a/elaborate.cc
+++ b/elaborate.cc
@@ -1781,10 +1781,8 @@ unsigned PGModule::calculate_instance_count_(Design*des, NetScope*scope,
 	 * I am expected to make more than one gate. Figure out how many are
 	 * desired. */
       if (msb_) {
-	    need_constant_expr = true;
-	    NetExpr*msb_exp = elab_and_eval(des, scope, msb_, -1);
-	    NetExpr*lsb_exp = elab_and_eval(des, scope, lsb_, -1);
-	    need_constant_expr = false;
+	    NetExpr*msb_exp = elab_and_eval(des, scope, msb_, -1, true);
+	    NetExpr*lsb_exp = elab_and_eval(des, scope, lsb_, -1, true);
 
 	    NetEConst*msb_con = dynamic_cast<NetEConst*>(msb_exp);
 	    NetEConst*lsb_con = dynamic_cast<NetEConst*>(lsb_exp);