diff --git a/crypto/zk/prover/pubsignals.go b/crypto/zk/prover/pubsignals.go
index 14f07c7a4..fd581b308 100644
--- a/crypto/zk/prover/pubsignals.go
+++ b/crypto/zk/prover/pubsignals.go
@@ -42,7 +42,7 @@ func (p *Proof) ElectionID() ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	return util.SplittedArboStrToBytes(electionID1str, electionID2str, false, false), nil
+	return util.SplittedArboStrToBytes(electionID1str, electionID2str, false, true), nil
 }
 
 // VoteHash returns the VoteHash included into the current proof.
diff --git a/util/zk.go b/util/zk.go
index 21f1164e8..c6e7187ee 100644
--- a/util/zk.go
+++ b/util/zk.go
@@ -54,10 +54,10 @@ func SplittedArboToBytes(input1, input2 *big.Int, swap, strict bool) []byte {
 	}
 	if strict {
 		for len(b1) < 16 {
-			b1 = append(b1, 0)
+			b1 = append([]byte{0}, b1...)
 		}
 		for len(b2) < 16 {
-			b2 = append(b2, 0)
+			b2 = append([]byte{0}, b2...)
 		}
 	}
 	return append(b1, b2...)