diff --git a/LaksaCsharp/Crypto/Schnorr.cs b/LaksaCsharp/Crypto/Schnorr.cs
index 7eb555f..d288521 100644
--- a/LaksaCsharp/Crypto/Schnorr.cs
+++ b/LaksaCsharp/Crypto/Schnorr.cs
@@ -135,6 +135,10 @@ public static bool Verify(byte[] msg, Signature sig, ECPoint publicKey)
                 throw new Exception("Invalid R or S value: cannot be negative.");
             }
 
+            if (sig.R.CompareTo(secp256k1.Curve.Order) >= 0 || sig.S.CompareTo(secp256k1.Curve.Order) >= 0) {
+                throw new Exception("Invalid R or S value: must be smaller than curve order");
+            }
+
             if (publicKey.Curve != (secp256k1.Curve))
             {
                 throw new Exception("The public key must be a point on secp256k1.");