diff --git a/crypto/mta/range_proof.go b/crypto/mta/range_proof.go
index 1c5b3a0e..dfd43257 100644
--- a/crypto/mta/range_proof.go
+++ b/crypto/mta/range_proof.go
@@ -141,6 +141,15 @@ func (pf *RangeProofAlice) Verify(ec elliptic.Curve, pk *paillier.PublicKey, NTi
 	if pf.S2.Cmp(q) == -1 {
 		return false
 	}
+	if pf.S.Cmp(one) == 0 {
+		return false
+	}
+	if pf.Z.Cmp(one) == 0 {
+		return false
+	}
+	if pf.S1.Cmp(pf.S2) == 0 {
+		return false
+	}
 
 	// 3.
 	if pf.S1.Cmp(q3) == 1 {