diff --git a/circuits/transaction.circom b/circuits/transaction.circom
index 2b16caa..e083c1e 100644
--- a/circuits/transaction.circom
+++ b/circuits/transaction.circom
@@ -130,4 +130,7 @@ template Transaction(levels, nIns, nOuts, zeroLeaf) {
     for (var i = 0; i < levels - 1; i++) {
         treeUpdater.pathElements[i] <== outPathElements[i];
     }
+
+    signal extDataSquare;
+    extDataSquare <== extDataHash * extDataHash;
 }