diff --git a/cmd/clef/tests/testsigner.js b/cmd/clef/tests/testsigner.js
index d2f25da31c..86b2c45395 100644
--- a/cmd/clef/tests/testsigner.js
+++ b/cmd/clef/tests/testsigner.js
@@ -28,7 +28,15 @@ init()
 function testTx(){
     if( accts && accts.length > 0) {
         var a = accts[0]
-        eth.signTransaction({from: a, to: a, value: 1, nonce: 1, gas: 1, gasPrice: 1})
+        var txdata = eth.signTransaction({from: a, to: a, value: 1, nonce: 1, gas: 1, gasPrice: 1})
+        var v = parseInt(txdata.tx.v)
+        console.log("V value: ", v)
+        if (v == 37 || v == 38){
+            console.log("Mainnet 155-protected chainid was used")
+        }
+        if (v == 27 || v == 28){
+            throw new Error("Mainnet chainid was used, but without replay protection!")
+        }
     }
 }
 function testSignText(){