diff --git a/project1/c.sql b/project1/c.sql
index c2f264a..70926c7 100644
--- a/project1/c.sql
+++ b/project1/c.sql
@@ -37,7 +37,7 @@ SELECT sig_id, pk_id
 FROM inputs 
 JOIN outputs 
 USING (tx_id)
-WHERE tx_id IN (SELECT tx_id FROM serial_control_transactions);
+WHERE tx_id IN (SELECT tx_id FROM serial_control_transactions) AND sig_id != 0;
 -------------------------------------
 -- clean up reflexivity
 DELETE