diff --git a/backends/btor/btor.cc b/backends/btor/btor.cc
index 2a98d1aba..51715ff25 100644
--- a/backends/btor/btor.cc
+++ b/backends/btor/btor.cc
@@ -334,7 +334,7 @@ struct BtorWorker
 
 				if (nid >= 0) {
 					int sid = get_bv_sid(width+upper-lower+1);
-					int nid4 = next_nid++;
+					nid4 = next_nid++;
 					btorf("%d concat %d %d %d\n", nid4, sid, nid, nid3);
 				}
 
@@ -411,8 +411,9 @@ struct BtorWorker
 
 			btorf_push(stringf("output %s", log_id(wire)));
 
+			int sid = get_bv_sid(GetSize(wire));
 			int nid = get_sig_nid(wire);
-			btorf("%d output %d %s\n", next_nid++, nid, log_id(wire));
+			btorf("%d output %d %d %s\n", next_nid++, sid, nid, log_id(wire));
 
 			btorf_pop(stringf("output %s", log_id(wire)));
 		}