diff --git a/index.js b/index.js
index 561c761..3ed1828 100644
--- a/index.js
+++ b/index.js
@@ -100,7 +100,7 @@ class Transaction {
     }, {
       name: 'v',
       allowZero: true,
-      default: new Buffer([0x1c])
+      default: new Buffer([opts.chain || opts.common ? this._common.chainId() : 0x1c])
     }, {
       name: 'r',
       length: 32,
@@ -184,10 +184,15 @@ class Transaction {
       // elements (i.e. nonce, gasprice, startgas, to, value, data), hash nine elements, with v replaced by
       // CHAIN_ID, r = 0 and s = 0.
 
-      const onEIP155BlockOrLater = this._common.gteHardfork('spuriousDragon')
       const v = ethUtil.bufferToInt(this.v)
+      const onEIP155BlockOrLater = this._common.gteHardfork('spuriousDragon')
       const vAndChainIdMeetEIP155Conditions = v === this._chainId * 2 + 35 || v === this._chainId * 2 + 36
-      if (vAndChainIdMeetEIP155Conditions && onEIP155BlockOrLater) {
+      const meetsAllEIP155Conditions = vAndChainIdMeetEIP155Conditions && onEIP155BlockOrLater
+
+      const unsigned = !this.r.length && !this.s.length
+      const seeksReplayProtection = this._chainId > 0
+
+      if (unsigned && seeksReplayProtection || !unsigned && meetsAllEIP155Conditions) {
         const raw = this.raw.slice()
         this.v = this._chainId
         this.r = 0
@@ -229,8 +234,8 @@ class Transaction {
    * @return {Buffer}
    */
   getSenderPublicKey () {
-    if (!this._senderPubKey || !this._senderPubKey.length) {
-      if (!this.verifySignature()) throw new Error('Invalid Signature')
+    if (!this.verifySignature()) {
+      throw new Error('Invalid Signature')
     }
     return this._senderPubKey
   }
diff --git a/test/api.js b/test/api.js
index c1a68ad..353d223 100644
--- a/test/api.js
+++ b/test/api.js
@@ -8,7 +8,7 @@ tape('[Transaction]: Basic functions', function (t) {
   var transactions = []
 
   t.test('should decode transactions', function (st) {
-    txFixtures.slice(0, 3).forEach(function (tx) {
+    txFixtures.slice(0, 4).forEach(function (tx) {
       var pt = new Transaction(tx.raw)
       st.equal('0x' + pt.nonce.toString('hex'), tx.raw[0])
       st.equal('0x' + pt.gasPrice.toString('hex'), tx.raw[1])
@@ -32,7 +32,7 @@ tape('[Transaction]: Basic functions', function (t) {
   })
 
   t.test('should hash', function (st) {
-    var tx = new Transaction(txFixtures[2].raw)
+    var tx = new Transaction(txFixtures[3].raw)
     st.deepEqual(tx.hash(), new Buffer('375a8983c9fc56d7cfd118254a80a8d7403d590a6c9e105532b67aca1efb97aa', 'hex'))
     st.deepEqual(tx.hash(false), new Buffer('61e1ec33764304dddb55348e7883d4437426f44ab3ef65e6da1e025734c03ff0', 'hex'))
     st.deepEqual(tx.hash(true), new Buffer('375a8983c9fc56d7cfd118254a80a8d7403d590a6c9e105532b67aca1efb97aa', 'hex'))
@@ -40,7 +40,7 @@ tape('[Transaction]: Basic functions', function (t) {
   })
 
   t.test('should hash with defined chainId', function (st) {
-    var tx = new Transaction(txFixtures[3].raw)
+    var tx = new Transaction(txFixtures[4].raw)
     st.equal(tx.hash().toString('hex'), '0f09dc98ea85b7872f4409131a790b91e7540953992886fc268b7ba5c96820e4')
     st.equal(tx.hash(true).toString('hex'), '0f09dc98ea85b7872f4409131a790b91e7540953992886fc268b7ba5c96820e4')
     st.equal(tx.hash(false).toString('hex'), 'f97c73fdca079da7652dbc61a46cd5aeef804008e057be3e712c43eac389aaf0')
@@ -153,7 +153,7 @@ tape('[Transaction]: Basic functions', function (t) {
     var tx = new Transaction()
     st.equals(tx.getDataFee().toNumber(), 0)
 
-    tx = new Transaction(txFixtures[2].raw)
+    tx = new Transaction(txFixtures[3].raw)
     st.equals(tx.getDataFee().toNumber(), 2496)
 
     st.end()
@@ -185,6 +185,42 @@ tape('[Transaction]: Basic functions', function (t) {
     st.end()
   })
 
+  t.test('Verify EIP155 Signature before and after signing with private key', function (st) {
+    // Inputs and expected results for this test are taken directly from the example in https://github.com/ethereum/EIPs/blob/master/EIPS/eip-155.md
+    var txRaw = [
+      '0x09',
+      '0x4a817c800',
+      '0x5208',
+      '0x3535353535353535353535353535353535353535',
+      '0x0de0b6b3a7640000',
+      '0x'
+    ]
+    var privateKey = Buffer.from('4646464646464646464646464646464646464646464646464646464646464646', 'hex')
+    var pt = new Transaction(txRaw, { chain: 1 })
+    st.equal(pt.serialize().toString('hex'), 'ec098504a817c800825208943535353535353535353535353535353535353535880de0b6b3a764000080018080')
+    pt.sign(privateKey)
+    st.equal(pt.hash(false).toString('hex'), 'daf5a779ae972f972197303d7b574746c7ef83eadac0f2791ad23db92e4c8e53')
+    st.equal(pt.serialize().toString('hex'), 'f86c098504a817c800825208943535353535353535353535353535353535353535880de0b6b3a76400008025a028ef61340bd939bc2195fe537567866003e1a15d3c71ff63e1590620aa636276a067cbe9d8997f761aecb703304b3800ccf555c9f3dc64214b297fb1966a3b6d83')
+    st.end()
+  })
+
+  t.test('Serialize correctly after being signed with EIP155 Signature for tx created on ropsten', function (st) {
+    var txRaw = [
+      '0x1',
+      '0x02540be400',
+      '0x5208',
+      '0xd7250824390ec5c8b71d856b5de895e271170d9d',
+      '0x0de0b6b3a7640000',
+      '0x'
+    ]
+
+    var privateKey = Buffer.from('DE3128752F183E8930D7F00A2AAA302DCB5E700B2CBA2D8CA5795660F07DEFD5', 'hex')
+    var pt = new Transaction(txRaw, { chain: 3 })
+    pt.sign(privateKey)
+    st.equal(pt.serialize().toString('hex'), 'f86c018502540be40082520894d7250824390ec5c8b71d856b5de895e271170d9d880de0b6b3a76400008029a0d3512c68099d184ccf54f44d9d6905bff303128574b663dcf10b4c726ddd8133a0628acc8f481dea593f13309dfc5f0340f83fdd40cf9fbe47f782668f6f3aec74')
+    st.end()
+  })
+
   t.test('sign tx with chainId specified in params', function (st) {
     var tx = new Transaction({ chainId: 42 })
     st.equal(tx.getChainId(), 42)
@@ -202,4 +238,21 @@ tape('[Transaction]: Basic functions', function (t) {
     st.equal(tx.getChainId(), 0x16b2)
     st.end()
   })
+
+  t.test('EIP155 hashing when singing', function (st) {
+    txFixtures.slice(0, 3).forEach(function (txData) {
+      const tx = new Transaction(txData.raw.slice(0, 6), {chain: 1})
+
+      var privKey = new Buffer(txData.privateKey, 'hex')
+      tx.sign(privKey)
+
+      st.equal(
+        tx.getSenderAddress().toString('hex'),
+        txData.sendersAddress,
+        'computed sender address should equal the fixture\'s one'
+      )
+    })
+
+    st.end()
+  })
 })
diff --git a/test/txs.json b/test/txs.json
index feb159b..2415383 100644
--- a/test/txs.json
+++ b/test/txs.json
@@ -14,6 +14,22 @@
     "0x5e1d3a76fbf824220eafc8c79ad578ad2b67d01b0c2425eb1f1347e8f50882ab",
     "0x5bd428537f05f9830e93792f90ea6a3e2d1ee84952dd96edbae9f658f831ab13"
   ]
+}, {
+  "privateKey": "4646464646464646464646464646464646464646464646464646464646464646",
+  "sendersAddress": "9d8a62f656a8d1615c1294fd71e9cfb3e4855a4f",
+  "type": "message",
+  "cost": 500,
+  "raw": [
+    "0x09",
+    "0x04a817c800",
+    "0x2710",
+    "0x3535353535353535353535353535353535353535",
+    "0x0de0b6b3a7640000",
+    "0x",
+    "0x25",
+    "0x28ef61340bd939bc2195fe537567866003e1a15d3c71ff63e1590620aa636276",
+    "0x67cbe9d8997f761aecb703304b3800ccf555c9f3dc64214b297fb1966a3b6d83"
+  ]
 }, {
   "privateKey": "e0a462586887362a18a318b128dbc1e3a0cae6d4b0739f5d0419ec25114bc722",
   "sendersAddress": "d13d825eb15c87b247c4c26331d66f225a5f632e",