diff --git a/contracts/Secp256r1.sol b/contracts/Secp256r1.sol
index 13d74ad..24bccfc 100644
--- a/contracts/Secp256r1.sol
+++ b/contracts/Secp256r1.sol
@@ -24,7 +24,7 @@ contract Secp256r1 {
     function Verify(uint X, uint Y, uint r, uint s, bytes memory input)
         public pure returns (bool)
     {
-        if (r >= nn || s >= nn) {
+        if (r==0 || s==0 ||r >= nn || s >= nn) {
             return false;
         }
 
@@ -321,4 +321,4 @@ contract Secp256r1 {
         return uint(t1);
     }
 
-}
\ No newline at end of file
+}