diff --git a/src/scripts.js b/src/scripts.js
index 661285a..88e3e61 100644
--- a/src/scripts.js
+++ b/src/scripts.js
@@ -238,9 +238,13 @@ function multisigInput(signatures, scriptPubKey) {
   if (scriptPubKey) {
     assert(isMultisigOutput.call(scriptPubKey))
 
-    var m = scriptPubKey.chunks[0]
-    var k = m - (opcodes.OP_1 - 1)
-    assert(k <= signatures.length, 'Not enough signatures provided')
+    var mOp = scriptPubKey.chunks[0]
+    var nOp = scriptPubKey.chunks[scriptPubKey.chunks.length - 2]
+    var m = mOp - (opcodes.OP_1 - 1)
+    var n = nOp - (opcodes.OP_1 - 1)
+
+    assert(signatures.length >= m, 'Not enough signatures provided')
+    assert(signatures.length <= n, 'Too many signatures provided')
   }
 
   return Script.fromChunks([].concat(opcodes.OP_0, signatures))
diff --git a/src/transaction.js b/src/transaction.js
index a9a0899..ffb9522 100644
--- a/src/transaction.js
+++ b/src/transaction.js
@@ -52,6 +52,7 @@ Transaction.prototype.addInput = function(tx, index, sequence) {
   assert(Buffer.isBuffer(hash), 'Expected Transaction, txId or txHash, got ' + tx)
   assert.equal(hash.length, 32, 'Expected hash length of 32, got ' + hash.length)
   assert.equal(typeof index, 'number', 'Expected number index, got ' + index)
+  assert.equal(typeof sequence, 'number', 'Expected number sequence, got ' + sequence)
 
   // Add the input and return the input's index
   return (this.ins.push({
diff --git a/src/transaction_builder.js b/src/transaction_builder.js
index 05c0591..c0acb09 100644
--- a/src/transaction_builder.js
+++ b/src/transaction_builder.js
@@ -30,10 +30,14 @@ TransactionBuilder.fromTransaction = function(transaction) {
   })
 
   // Extract/add signatures
-  transaction.ins.forEach(function(txin) {
+  transaction.ins.forEach(function(txin, i) {
     // Ignore empty scripts
     if (txin.script.buffer.length === 0) return
 
+    assert(!Array.prototype.every.call(txin.hash, function(x) {
+      return x === 0
+    }), 'coinbase inputs not supported')
+
     var redeemScript
     var scriptSig = txin.script
     var scriptType = scripts.classifyInput(scriptSig)
@@ -83,10 +87,10 @@ TransactionBuilder.fromTransaction = function(transaction) {
         break
 
       default:
-        assert(false, scriptType + ' not supported')
+        assert(false, scriptType + ' inputs not supported')
     }
 
-    txb.signatures[txin.index] = {
+    txb.signatures[i] = {
       hashType: hashType,
       pubKeys: pubKeys,
       redeemScript: redeemScript,
@@ -231,13 +235,18 @@ TransactionBuilder.prototype.sign = function(index, privKey, redeemScript, hashT
 
   } else {
     prevOutScript = prevOutScript || privKey.pub.getAddress().toOutputScript()
-    scriptType = prevOutType || 'pubkeyhash'
+    prevOutType = prevOutType || 'pubkeyhash'
 
-    assert.notEqual(scriptType, 'scripthash', 'PrevOutScript requires redeemScript')
+    assert.notEqual(prevOutType, 'scripthash', 'PrevOutScript is P2SH, missing redeemScript')
+
+    scriptType = prevOutType
 
     hash = this.tx.hashForSignature(index, prevOutScript, hashType)
   }
 
+  this.prevOutScripts[index] = prevOutScript
+  this.prevOutTypes[index] = prevOutType
+
   if (!(index in this.signatures)) {
     this.signatures[index] = {
       hashType: hashType,
@@ -246,6 +255,8 @@ TransactionBuilder.prototype.sign = function(index, privKey, redeemScript, hashT
       scriptType: scriptType,
       signatures: []
     }
+  } else {
+    assert.equal(scriptType, 'multisig', scriptType + ' doesn\'t support multiple signatures')
   }
 
   var input = this.signatures[index]
diff --git a/test/fixtures/scripts.json b/test/fixtures/scripts.json
index 666ea59..e264a4a 100644
--- a/test/fixtures/scripts.json
+++ b/test/fixtures/scripts.json
@@ -101,6 +101,19 @@
           "304402207515cf147d201f411092e6be5a64a6006f9308fad7b2a8fdaab22cd86ce764c202200974b8aca7bf51dbf54150d3884e1ae04f675637b926ec33bf75939446f6ca2801"
         ],
         "scriptPubKey": false
+      },
+      {
+        "exception": "Too many signatures provided",
+        "pubKeys": [
+          "02359c6e3f04cefbf089cf1d6670dc47c3fb4df68e2bad1fa5a369f9ce4b42bbd1",
+          "0395a9d84d47d524548f79f435758c01faec5da2b7e551d3b8c995b7e06326ae4a"
+        ],
+        "signatures": [
+          "304402207515cf147d201f411092e6be5a64a6006f9308fad7b2a8fdaab22cd86ce764c202200974b8aca7bf51dbf54150d3884e1ae04f675637b926ec33bf75939446f6ca2801",
+          "3045022100ef253c1faa39e65115872519e5f0a33bbecf430c0f35cf562beabbad4da24d8d02201742be8ee49812a73adea3007c9641ce6725c32cd44ddb8e3a3af460015d140501",
+          "3045022100ef253c1faa39e65115872519e5f0a33bbecf430c0f35cf562beabbad4da24d8d02201742be8ee49812a73adea3007c9641ce6725c32cd44ddb8e3a3af460015d140501"
+        ],
+        "scriptPubKey": false
       }
     ]
   }
diff --git a/test/fixtures/transaction_builder.json b/test/fixtures/transaction_builder.json
index c2444ea..a44078b 100644
--- a/test/fixtures/transaction_builder.json
+++ b/test/fixtures/transaction_builder.json
@@ -63,6 +63,26 @@
             "value": 10000
           }
         ]
+      },
+      {
+        "description": "Transaction w/ non-zero vin inputs",
+        "txid": "7d9b699f26765fdfdd598223a952a6e129f8c159e2e05e911af822ee743fa745",
+        "txhex": "0100000001ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff010000006a47304402205c80bbb5125b35d5e5a8324b1336832d29a6fc004859c8a9ff6bef47ba7fc348022018612216e57a521b2c4543f1f4fd738a76814c37c074e88adfe12464fff31cf901210279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798ffffffff0110270000000000001976a914aa4d7985c57e011a8b3dd8e0e5a73aaef41629c588ac00000000",
+        "inputs": [
+          {
+            "index": 1,
+            "prevTx": "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
+            "privKeys": [
+              "KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn"
+            ]
+          }
+        ],
+        "outputs": [
+          {
+            "script": "OP_DUP OP_HASH160 aa4d7985c57e011a8b3dd8e0e5a73aaef41629c5 OP_EQUALVERIFY OP_CHECKSIG",
+            "value": 10000
+          }
+        ]
       }
     ]
   },
@@ -147,6 +167,16 @@
           }
         ]
       }
+    ],
+    "fromTransaction": [
+      {
+        "exception": "coinbase inputs not supported",
+        "hex":"01000000010000000000000000000000000000000000000000000000000000000000000000000000006b483045022100a3b254e1c10b5d039f36c05f323995d6e5a367d98dd78a13d5bbc3991b35720e022022fccea3897d594de0689601fbd486588d5bfa6915be2386db0397ee9a6e80b601210279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798ffffffff0110270000000000001976a914aa4d7985c57e011a8b3dd8e0e5a73aaef41629c588ac00000000" 
+      },
+      {
+        "exception": "nonstandard inputs not supported",
+        "hex": "0100000001ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff0000000023aa206fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d619000000000087ffffffff0110270000000000001976a914aa4d7985c57e011a8b3dd8e0e5a73aaef41629c588ac00000000" 
+      }
     ]
   }
 }
diff --git a/test/transaction_builder.js b/test/transaction_builder.js
index d6ab2f0..0bc1032 100644
--- a/test/transaction_builder.js
+++ b/test/transaction_builder.js
@@ -110,6 +110,27 @@ describe('TransactionBuilder', function() {
       })
     })
 
+    it('throws if scriptType doesn\'t support multiple signatures', function() {
+      txb.addInput(prevTxHash, 0)
+      txb.sign(0, privKey)
+
+      assert.throws(function() {
+        txb.sign(0, privKey)
+      }, /pubkeyhash doesn\'t support multiple signatures/)
+    })
+
+    describe('when redeemScript is undefined', function() {
+      it('throws if prevOutScript is P2SH', function() {
+        var privScriptP2SH = scripts.scriptHashOutput(privScript.getHash())
+
+        txb.addInput(prevTxHash, 0, undefined, privScriptP2SH)
+
+        assert.throws(function() {
+          txb.sign(0, privKey)
+        }, /PrevOutScript is P2SH, missing redeemScript/)
+      })
+    })
+
     describe('when redeemScript is defined', function() {
       it('assumes scriptHash', function() {
         txb.addInput(prevTxHash, 0)
@@ -182,6 +203,7 @@ describe('TransactionBuilder', function() {
         var tx = txb.build()
 
         assert.equal(tx.getId(), f.txid)
+        assert.equal(tx.toHex(), f.txhex)
       })
     })
 
@@ -234,6 +256,16 @@ describe('TransactionBuilder', function() {
       })
     })
 
+    fixtures.invalid.fromTransaction.forEach(function(f,i) {
+      it('throws on ' + f.exception, function() {
+        var tx = Transaction.fromHex(f.hex)
+
+        assert.throws(function() {
+          TransactionBuilder.fromTransaction(tx)
+        }, new RegExp(f.exception))
+      })
+    })
+
     it('works for the P2SH multisig case', function() {
       var privKeys = [
         "91avARGdfge8E4tZfYLoxeJ5sGBdNJQH4kvjJoQFacbgwmaKkrx",