diff --git a/src/address.ts b/src/address.ts
index f273b43..c9ffeeb 100644
--- a/src/address.ts
+++ b/src/address.ts
@@ -75,8 +75,8 @@ export function fromOutputScript (output: Buffer, network: Network): string { //
 export function toOutputScript (address: string, network: Network): Buffer {
   network = network || networks.bitcoin
 
-  let decodeBase58: Base58CheckResult
-  let decodeBech32: Bech32Result
+  let decodeBase58: Base58CheckResult | undefined = undefined
+  let decodeBech32: Bech32Result | undefined = undefined
   try {
     decodeBase58 = fromBase58Check(address)
   } catch (e) {}
diff --git a/src/ecpair.ts b/src/ecpair.ts
index cb835d1..a7426ae 100644
--- a/src/ecpair.ts
+++ b/src/ecpair.ts
@@ -20,8 +20,8 @@ interface ECPairOptions {
 export interface ECPairInterface {
   compressed: boolean
   network: Network
-  privateKey: Buffer
-  publicKey: Buffer
+  privateKey: Buffer | null
+  publicKey: Buffer | null
   toWIF(): string
   sign(hash: Buffer): Buffer
   verify(hash: Buffer, signature: Buffer): Buffer
@@ -31,9 +31,9 @@ export interface ECPairInterface {
 class ECPair implements ECPairInterface {
   compressed: boolean
   network: Network
-  private __d: Buffer
-  private __Q: Buffer
-  constructor (d: Buffer | void, Q: Buffer | void, options: ECPairOptions) {
+  private __d: Buffer | null
+  private __Q: Buffer | null
+  constructor (d: Buffer | null, Q: Buffer | null, options: ECPairOptions) {
     if (options === undefined) options = {}
     this.compressed = options.compressed === undefined ? true : options.compressed
     this.network = options.network || NETWORKS.bitcoin
@@ -43,11 +43,11 @@ class ECPair implements ECPairInterface {
     if (Q) this.__Q = ecc.pointCompress(Q, this.compressed)
   }
 
-  get privateKey (): Buffer {
+  get privateKey (): Buffer | null {
     return this.__d
   }
 
-  get publicKey (): Buffer {
+  get publicKey (): Buffer | null {
     if (!this.__Q) this.__Q = ecc.pointFromScalar(this.__d, this.compressed)
     return this.__Q
   }
@@ -87,7 +87,7 @@ function fromWIF (string: string, network: Network | Array<Network>): ECPair {
 
   // list of networks?
   if (types.Array(network)) {
-    network = (<Array<Network>>network).filter(function (x: Network) {
+    network = <Network>(<Array<Network>>network).filter(function (x: Network) {
       return version === x.wif
     }).pop()
 
diff --git a/src/payments/embed.ts b/src/payments/embed.ts
index a28747f..2526fe0 100644
--- a/src/payments/embed.ts
+++ b/src/payments/embed.ts
@@ -36,17 +36,17 @@ export function p2data (a: Payment, opts: PaymentOpts): Payment {
   })
   lazy.prop(o, 'data', function () {
     if (!a.output) return
-    return bscript.decompile(a.output).slice(1)
+    return (<Array<Buffer | number>>bscript.decompile(a.output)).slice(1)
   })
 
   // extended validation
   if (opts.validate) {
     if (a.output) {
       const chunks = bscript.decompile(a.output)
-      if (chunks[0] !== OPS.OP_RETURN) throw new TypeError('Output is invalid')
-      if (!chunks.slice(1).every(typef.Buffer)) throw new TypeError('Output is invalid')
+      if ((<Array<Buffer | number>>chunks)[0] !== OPS.OP_RETURN) throw new TypeError('Output is invalid')
+      if (!(<Array<Buffer | number>>chunks).slice(1).every(typef.Buffer)) throw new TypeError('Output is invalid')
 
-      if (a.data && !stacksEqual(a.data, o.data)) throw new TypeError('Data mismatch')
+      if (a.data && !stacksEqual(a.data, <Array<Buffer>>o.data)) throw new TypeError('Data mismatch')
     }
   }
 
diff --git a/src/payments/lazy.ts b/src/payments/lazy.ts
index 6a4cbe3..1d4af68 100644
--- a/src/payments/lazy.ts
+++ b/src/payments/lazy.ts
@@ -20,7 +20,7 @@ export function prop (object: Object, name: string, f: ()=>any): void {
 
 export function value <T>(f: ()=>T): ()=>T {
   let value: T
-  return function () {
+  return function (): T {
     if (value !== undefined) return value
     value = f()
     return value
diff --git a/src/payments/p2ms.ts b/src/payments/p2ms.ts
index 2142ff1..b8a05b3 100644
--- a/src/payments/p2ms.ts
+++ b/src/payments/p2ms.ts
@@ -28,7 +28,7 @@ export function p2ms (a: Payment, opts: PaymentOpts): Payment {
   opts = Object.assign({ validate: true }, opts || {})
 
   function isAcceptableSignature (x: Buffer | number) {
-    return bscript.isCanonicalScriptSignature(<Buffer>x) || (opts.allowIncomplete && (<number>x === OPS.OP_0))
+    return bscript.isCanonicalScriptSignature(<Buffer>x) || (opts.allowIncomplete && (<number>x === OPS.OP_0)) !== undefined
   }
 
   typef({
@@ -45,12 +45,12 @@ export function p2ms (a: Payment, opts: PaymentOpts): Payment {
   const network = a.network || BITCOIN_NETWORK
   const o: Payment = { network }
 
-  let chunks: Array<Buffer | number>
+  let chunks: Array<Buffer | number> = []
   let decoded = false
   function decode (output: Buffer | Array<Buffer | number>): void {
     if (decoded) return
     decoded = true
-    chunks = bscript.decompile(output)
+    chunks = <Array<Buffer | number>>bscript.decompile(output)
     o.m = <number>chunks[0] - OP_INT_BASE
     o.n = <number>chunks[chunks.length - 2] - OP_INT_BASE
     o.pubkeys = <Array<Buffer>>chunks.slice(1, -2)
@@ -60,7 +60,7 @@ export function p2ms (a: Payment, opts: PaymentOpts): Payment {
     if (!a.m) return
     if (!o.n) return
     if (!a.pubkeys) return
-    return bscript.compile([].concat(
+    return bscript.compile((<Array<Buffer | number>>[]).concat(
       OP_INT_BASE + a.m,
       a.pubkeys,
       OP_INT_BASE + o.n,
@@ -83,7 +83,7 @@ export function p2ms (a: Payment, opts: PaymentOpts): Payment {
   })
   lazy.prop(o, 'signatures', function () {
     if (!a.input) return
-    return bscript.decompile(a.input).slice(1)
+    return (<Array<Buffer | number>>bscript.decompile(a.input)).slice(1)
   })
   lazy.prop(o, 'input', function () {
     if (!a.signatures) return
@@ -103,35 +103,35 @@ export function p2ms (a: Payment, opts: PaymentOpts): Payment {
       if (chunks[chunks.length - 1] !== OPS.OP_CHECKMULTISIG) throw new TypeError('Output is invalid')
 
       if (
-        o.m <= 0 ||
-        o.n > 16 ||
-        o.m > o.n ||
+        <number>(<Payment>o).m <= 0 ||
+        <number>(<Payment>o).n > 16 ||
+        <number>(<Payment>o).m > <number>(<Payment>o).n ||
         o.n !== chunks.length - 3) throw new TypeError('Output is invalid')
-      if (!o.pubkeys.every(x => ecc.isPoint(x))) throw new TypeError('Output is invalid')
+      if (!(<Array<Buffer>>o.pubkeys).every(x => ecc.isPoint(x))) throw new TypeError('Output is invalid')
 
       if (a.m !== undefined && a.m !== o.m) throw new TypeError('m mismatch')
       if (a.n !== undefined && a.n !== o.n) throw new TypeError('n mismatch')
-      if (a.pubkeys && !stacksEqual(a.pubkeys, o.pubkeys)) throw new TypeError('Pubkeys mismatch')
+      if (a.pubkeys && !stacksEqual(a.pubkeys, (<Array<Buffer>>o.pubkeys))) throw new TypeError('Pubkeys mismatch')
     }
 
     if (a.pubkeys) {
       if (a.n !== undefined && a.n !== a.pubkeys.length) throw new TypeError('Pubkey count mismatch')
       o.n = a.pubkeys.length
 
-      if (o.n < o.m) throw new TypeError('Pubkey count cannot be less than m')
+      if (o.n < <number>(<Payment>o).m) throw new TypeError('Pubkey count cannot be less than m')
     }
 
     if (a.signatures) {
-      if (a.signatures.length < o.m) throw new TypeError('Not enough signatures provided')
-      if (a.signatures.length > o.m) throw new TypeError('Too many signatures provided')
+      if (a.signatures.length < <number>(<Payment>o).m) throw new TypeError('Not enough signatures provided')
+      if (a.signatures.length > <number>(<Payment>o).m) throw new TypeError('Too many signatures provided')
     }
 
     if (a.input) {
       if (a.input[0] !== OPS.OP_0) throw new TypeError('Input is invalid')
-      if (o.signatures.length === 0 || !o.signatures.every(isAcceptableSignature)) throw new TypeError('Input has invalid signature(s)')
+      if ((<Array<Buffer>>o.signatures).length === 0 || !(<Array<Buffer>>o.signatures).every(isAcceptableSignature)) throw new TypeError('Input has invalid signature(s)')
 
-      if (a.signatures && !stacksEqual(a.signatures, o.signatures)) throw new TypeError('Signature mismatch')
-      if (a.m !== undefined && a.m !== a.signatures.length) throw new TypeError('Signature count mismatch')
+      if (a.signatures && !stacksEqual(a.signatures, (<Array<Buffer>>o.signatures))) throw new TypeError('Signature mismatch')
+      if (a.m !== undefined && a.m !== (<Array<Buffer>>a.signatures).length) throw new TypeError('Signature count mismatch')
     }
   }
 
diff --git a/src/payments/p2pk.ts b/src/payments/p2pk.ts
index a1ac5e8..45b3577 100644
--- a/src/payments/p2pk.ts
+++ b/src/payments/p2pk.ts
@@ -27,7 +27,7 @@ export function p2pk (a: Payment, opts: PaymentOpts): Payment {
     input: typef.maybe(typef.Buffer)
   }, a)
 
-  const _chunks = lazy.value(function () { return bscript.decompile(a.input) })
+  const _chunks = <()=>Array<Buffer | number>>lazy.value(function () { return bscript.decompile(<Buffer>a.input) })
 
   const network = a.network || BITCOIN_NETWORK
   const o: Payment = { network }
@@ -45,7 +45,7 @@ export function p2pk (a: Payment, opts: PaymentOpts): Payment {
   })
   lazy.prop(o, 'signature', function () {
     if (!a.input) return
-    return _chunks()[0]
+    return <Buffer>_chunks()[0]
   })
   lazy.prop(o, 'input', function () {
     if (!a.signature) return
@@ -61,16 +61,16 @@ export function p2pk (a: Payment, opts: PaymentOpts): Payment {
     if (a.output) {
       if (a.output[a.output.length - 1] !== OPS.OP_CHECKSIG) throw new TypeError('Output is invalid')
       if (!ecc.isPoint(o.pubkey)) throw new TypeError('Output pubkey is invalid')
-      if (a.pubkey && !a.pubkey.equals(o.pubkey)) throw new TypeError('Pubkey mismatch')
+      if (a.pubkey && !a.pubkey.equals(<Buffer>o.pubkey)) throw new TypeError('Pubkey mismatch')
     }
 
     if (a.signature) {
-      if (a.input && !a.input.equals(o.input)) throw new TypeError('Signature mismatch')
+      if (a.input && !a.input.equals(<Buffer>o.input)) throw new TypeError('Signature mismatch')
     }
 
     if (a.input) {
       if (_chunks().length !== 1) throw new TypeError('Input is invalid')
-      if (!bscript.isCanonicalScriptSignature(o.signature)) throw new TypeError('Input has invalid signature')
+      if (!bscript.isCanonicalScriptSignature(<Buffer>o.signature)) throw new TypeError('Input has invalid signature')
     }
   }
 
diff --git a/src/payments/p2pkh.ts b/src/payments/p2pkh.ts
index e32f933..f2054b0 100644
--- a/src/payments/p2pkh.ts
+++ b/src/payments/p2pkh.ts
@@ -38,7 +38,7 @@ export function p2pkh (a: Payment, opts: PaymentOpts): Payment {
     const hash = payload.slice(1)
     return { version, hash }
   })
-  const _chunks = lazy.value(function () { return bscript.decompile(a.input) })
+  const _chunks = <()=>Array<Buffer | number>>lazy.value(function () { return bscript.decompile(<Buffer>a.input) })
 
   const network = a.network || BITCOIN_NETWORK
   const o: Payment = { network }
@@ -54,7 +54,7 @@ export function p2pkh (a: Payment, opts: PaymentOpts): Payment {
   lazy.prop(o, 'hash', function () {
     if (a.output) return a.output.slice(3, 23)
     if (a.address) return _address().hash
-    if (a.pubkey || o.pubkey) return bcrypto.hash160(a.pubkey || o.pubkey)
+    if (a.pubkey || o.pubkey) return bcrypto.hash160(<Buffer>a.pubkey || <Buffer>o.pubkey)
   })
   lazy.prop(o, 'output', function () {
     if (!o.hash) return
@@ -68,11 +68,11 @@ export function p2pkh (a: Payment, opts: PaymentOpts): Payment {
   })
   lazy.prop(o, 'pubkey', function () {
     if (!a.input) return
-    return _chunks()[1]
+    return <Buffer>_chunks()[1]
   })
   lazy.prop(o, 'signature', function () {
     if (!a.input) return
-    return _chunks()[0]
+    return <Buffer>_chunks()[0]
   })
   lazy.prop(o, 'input', function () {
     if (!a.pubkey) return
@@ -86,7 +86,7 @@ export function p2pkh (a: Payment, opts: PaymentOpts): Payment {
 
   // extended validation
   if (opts.validate) {
-    let hash: Buffer
+    let hash: Buffer = Buffer.from([])
     if (a.address) {
       if (_address().version !== network.pubKeyHash) throw new TypeError('Invalid version or Network mismatch')
       if (_address().hash.length !== 20) throw new TypeError('Invalid address')
@@ -94,7 +94,7 @@ export function p2pkh (a: Payment, opts: PaymentOpts): Payment {
     }
 
     if (a.hash) {
-      if (hash && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
       else hash = a.hash
     }
 
@@ -108,13 +108,13 @@ export function p2pkh (a: Payment, opts: PaymentOpts): Payment {
         a.output[24] !== OPS.OP_CHECKSIG) throw new TypeError('Output is invalid')
 
       const hash2 = a.output.slice(3, 23)
-      if (hash && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
       else hash = hash2
     }
 
     if (a.pubkey) {
       const pkh = bcrypto.hash160(a.pubkey)
-      if (hash && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
       else hash = pkh
     }
 
@@ -128,7 +128,7 @@ export function p2pkh (a: Payment, opts: PaymentOpts): Payment {
       if (a.pubkey && !a.pubkey.equals(<Buffer>chunks[1])) throw new TypeError('Pubkey mismatch')
 
       const pkh = bcrypto.hash160(<Buffer>chunks[1])
-      if (hash && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
     }
   }
 
diff --git a/src/payments/p2sh.ts b/src/payments/p2sh.ts
index 2219f33..6facde9 100644
--- a/src/payments/p2sh.ts
+++ b/src/payments/p2sh.ts
@@ -1,4 +1,5 @@
 import { Payment, PaymentOpts } from './index'
+import { Network } from '../networks'
 import * as bscript from '../script'
 import * as bcrypto from '../crypto'
 import * as lazy from './lazy'
@@ -59,7 +60,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
     const hash = payload.slice(1)
     return { version, hash }
   })
-  const _chunks = lazy.value(function () { return bscript.decompile(a.input) })
+  const _chunks = <()=>Array<Buffer | number>>lazy.value(function () { return bscript.decompile(<Buffer>a.input) })
   const _redeem = lazy.value(function (): Payment {
     const chunks = _chunks()
     return {
@@ -75,7 +76,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
     if (!o.hash) return
 
     const payload = Buffer.allocUnsafe(21)
-    payload.writeUInt8(network.scriptHash, 0)
+    payload.writeUInt8((<Network>o.network).scriptHash, 0)
     o.hash.copy(payload, 1)
     return bs58check.encode(payload)
   })
@@ -101,8 +102,8 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
   })
   lazy.prop(o, 'input', function () {
     if (!a.redeem || !a.redeem.input || !a.redeem.output) return
-    return bscript.compile([].concat(
-      bscript.decompile(a.redeem.input),
+    return bscript.compile((<Array<Buffer | number>>[]).concat(
+      <Array<Buffer | number>>bscript.decompile(a.redeem.input),
       a.redeem.output
     ))
   })
@@ -112,7 +113,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
   })
 
   if (opts.validate) {
-    let hash: Buffer
+    let hash: Buffer = Buffer.from([])
     if (a.address) {
       if (_address().version !== network.scriptHash) throw new TypeError('Invalid version or Network mismatch')
       if (_address().hash.length !== 20) throw new TypeError('Invalid address')
@@ -120,7 +121,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
     }
 
     if (a.hash) {
-      if (hash && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
       else hash = a.hash
     }
 
@@ -132,7 +133,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
         a.output[22] !== OPS.OP_EQUAL) throw new TypeError('Output is invalid')
 
       const hash2 = a.output.slice(2, 22)
-      if (hash && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
       else hash = hash2
     }
 
@@ -145,7 +146,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
 
         // match hash against other sources
         const hash2 = bcrypto.hash160(redeem.output)
-        if (hash && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
+        if (hash.length > 0 && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
         else hash = hash2
       }
 
@@ -155,7 +156,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
         if (!hasInput && !hasWitness) throw new TypeError('Empty input')
         if (hasInput && hasWitness) throw new TypeError('Input and witness provided')
         if (hasInput) {
-          const richunks = bscript.decompile(redeem.input)
+          const richunks = <Array<Buffer | number>>bscript.decompile(redeem.input)
           if (!bscript.isPushOnly(richunks)) throw new TypeError('Non push-only scriptSig')
         }
       }
@@ -174,7 +175,7 @@ export function p2sh (a: Payment, opts: PaymentOpts): Payment {
       if (a.input) {
         const redeem = _redeem()
         if (a.redeem.output && !a.redeem.output.equals(<Buffer>redeem.output)) throw new TypeError('Redeem.output mismatch')
-        if (a.redeem.input && !a.redeem.input.equals(redeem.input)) throw new TypeError('Redeem.input mismatch')
+        if (a.redeem.input && !a.redeem.input.equals(<Buffer>redeem.input)) throw new TypeError('Redeem.input mismatch')
       }
 
       checkRedeem(a.redeem)
diff --git a/src/payments/p2wpkh.ts b/src/payments/p2wpkh.ts
index a25d037..7089246 100644
--- a/src/payments/p2wpkh.ts
+++ b/src/payments/p2wpkh.ts
@@ -59,7 +59,7 @@ export function p2wpkh (a: Payment, opts: PaymentOpts): Payment {
   lazy.prop(o, 'hash', function () {
     if (a.output) return a.output.slice(2, 22)
     if (a.address) return _address().data
-    if (a.pubkey || o.pubkey) return bcrypto.hash160(a.pubkey || o.pubkey)
+    if (a.pubkey || o.pubkey) return bcrypto.hash160(<Buffer>a.pubkey || <Buffer>o.pubkey)
   })
   lazy.prop(o, 'output', function () {
     if (!o.hash) return
@@ -89,7 +89,7 @@ export function p2wpkh (a: Payment, opts: PaymentOpts): Payment {
 
   // extended validation
   if (opts.validate) {
-    let hash: Buffer
+    let hash: Buffer = Buffer.from([])
     if (a.address) {
       if (network && network.bech32 !== _address().prefix) throw new TypeError('Invalid prefix or Network mismatch')
       if (_address().version !== 0x00) throw new TypeError('Invalid address version')
@@ -98,7 +98,7 @@ export function p2wpkh (a: Payment, opts: PaymentOpts): Payment {
     }
 
     if (a.hash) {
-      if (hash && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
       else hash = a.hash
     }
 
@@ -107,13 +107,13 @@ export function p2wpkh (a: Payment, opts: PaymentOpts): Payment {
         a.output.length !== 22 ||
         a.output[0] !== OPS.OP_0 ||
         a.output[1] !== 0x14) throw new TypeError('Output is invalid')
-      if (hash && !hash.equals(a.output.slice(2))) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(a.output.slice(2))) throw new TypeError('Hash mismatch')
       else hash = a.output.slice(2)
     }
 
     if (a.pubkey) {
       const pkh = bcrypto.hash160(a.pubkey)
-      if (hash && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
       else hash = pkh
     }
 
@@ -126,7 +126,7 @@ export function p2wpkh (a: Payment, opts: PaymentOpts): Payment {
       if (a.pubkey && !a.pubkey.equals(a.witness[1])) throw new TypeError('Pubkey mismatch')
 
       const pkh = bcrypto.hash160(a.witness[1])
-      if (hash && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(pkh)) throw new TypeError('Hash mismatch')
     }
   }
 
diff --git a/src/payments/p2wsh.ts b/src/payments/p2wsh.ts
index d94d446..c70cfb6 100644
--- a/src/payments/p2wsh.ts
+++ b/src/payments/p2wsh.ts
@@ -1,4 +1,5 @@
 import { Payment, PaymentOpts } from './index'
+import { Network } from '../networks'
 import * as bscript from '../script'
 import * as bcrypto from '../crypto'
 import * as lazy from './lazy'
@@ -58,7 +59,7 @@ export function p2wsh (a: Payment, opts: PaymentOpts): Payment {
       data: Buffer.from(data)
     }
   })
-  const _rchunks = lazy.value(function () { return bscript.decompile(a.redeem.input) })
+  const _rchunks = <()=>Array<Buffer | number>>lazy.value(function () { return bscript.decompile(<Buffer>(<Payment>a.redeem).input) })
 
   let network = a.network
   if (!network) {
@@ -71,7 +72,7 @@ export function p2wsh (a: Payment, opts: PaymentOpts): Payment {
     if (!o.hash) return
     const words = bech32.toWords(o.hash)
     words.unshift(0x00)
-    return bech32.encode(network.bech32, words)
+    return bech32.encode((<Network>network).bech32, words)
   })
   lazy.prop(o, 'hash', function () {
     if (a.output) return a.output.slice(2)
@@ -111,18 +112,18 @@ export function p2wsh (a: Payment, opts: PaymentOpts): Payment {
       // assign, and blank the existing input
       o.redeem = Object.assign({ witness: stack }, a.redeem)
       o.redeem.input = EMPTY_BUFFER
-      return [].concat(stack, a.redeem.output)
+      return (<Array<Buffer>>[]).concat(stack, a.redeem.output)
     }
 
     if (!a.redeem) return
     if (!a.redeem.output) return
     if (!a.redeem.witness) return
-    return [].concat(a.redeem.witness, a.redeem.output)
+    return (<Array<Buffer>>[]).concat(a.redeem.witness, a.redeem.output)
   })
 
   // extended validation
   if (opts.validate) {
-    let hash: Buffer
+    let hash: Buffer = Buffer.from([])
     if (a.address) {
       if (_address().prefix !== network.bech32) throw new TypeError('Invalid prefix or Network mismatch')
       if (_address().version !== 0x00) throw new TypeError('Invalid address version')
@@ -131,7 +132,7 @@ export function p2wsh (a: Payment, opts: PaymentOpts): Payment {
     }
 
     if (a.hash) {
-      if (hash && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(a.hash)) throw new TypeError('Hash mismatch')
       else hash = a.hash
     }
 
@@ -141,7 +142,7 @@ export function p2wsh (a: Payment, opts: PaymentOpts): Payment {
         a.output[0] !== OPS.OP_0 ||
         a.output[1] !== 0x20) throw new TypeError('Output is invalid')
       const hash2 = a.output.slice(2)
-      if (hash && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
+      if (hash.length > 0 && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
       else hash = hash2
     }
 
@@ -158,11 +159,11 @@ export function p2wsh (a: Payment, opts: PaymentOpts): Payment {
 
       // is the redeem output non-empty?
       if (a.redeem.output) {
-        if (bscript.decompile(a.redeem.output).length === 0) throw new TypeError('Redeem.output is invalid')
+        if ((<Array<Buffer | number>>bscript.decompile(a.redeem.output)).length === 0) throw new TypeError('Redeem.output is invalid')
 
         // match hash against other sources
         const hash2 = bcrypto.sha256(a.redeem.output)
-        if (hash && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
+        if (hash.length > 0 && !hash.equals(hash2)) throw new TypeError('Hash mismatch')
         else hash = hash2
       }
 
diff --git a/src/script.ts b/src/script.ts
index 88bc46e..6d9bfc9 100644
--- a/src/script.ts
+++ b/src/script.ts
@@ -94,7 +94,7 @@ export function compile (chunks: Buffer | Array<number | Buffer>): Buffer {
   return buffer
 }
 
-export function decompile (buffer: Buffer | Array<number | Buffer>): Array<number | Buffer> {
+export function decompile (buffer: Buffer | Array<number | Buffer>): Array<number | Buffer> | null {
   // TODO: remove me
   if (chunksIsArray(buffer)) return buffer
 
@@ -141,7 +141,7 @@ export function decompile (buffer: Buffer | Array<number | Buffer>): Array<numbe
 
 export function toASM (chunks: Buffer | Array<number | Buffer>): string {
   if (chunksIsBuffer(chunks)) {
-    chunks = decompile(chunks)
+    chunks = <Array<number | Buffer>>decompile(chunks)
   }
 
   return chunks.map(function (chunk) {
@@ -171,7 +171,7 @@ export function fromASM (asm: string): Buffer {
 }
 
 export function toStack (chunks: Buffer | Array<number | Buffer>): Array<Buffer> {
-  chunks = decompile(chunks)
+  chunks = <Array<number | Buffer>>decompile(chunks)
   typeforce(isPushOnly, chunks)
 
   return chunks.map(function (op) {
diff --git a/src/templates/multisig/input.ts b/src/templates/multisig/input.ts
index 2060242..abf0982 100644
--- a/src/templates/multisig/input.ts
+++ b/src/templates/multisig/input.ts
@@ -8,7 +8,7 @@ function partialSignature (value: number | Buffer): boolean {
 }
 
 export function check (script: Buffer | Array<number | Buffer>, allowIncomplete?: boolean): boolean {
-  const chunks = bscript.decompile(script)
+  const chunks = <Array<number | Buffer>>bscript.decompile(script)
   if (chunks.length < 2) return false
   if (chunks[0] !== OPS.OP_0) return false
 
diff --git a/src/templates/multisig/output.ts b/src/templates/multisig/output.ts
index 50c701e..e4fa333 100644
--- a/src/templates/multisig/output.ts
+++ b/src/templates/multisig/output.ts
@@ -6,7 +6,7 @@ const OPS = require('bitcoin-ops')
 const OP_INT_BASE = OPS.OP_RESERVED // OP_1 - 1
 
 export function check (script: Buffer | Array<number | Buffer>, allowIncomplete?: boolean): boolean {
-  const chunks = bscript.decompile(script)
+  const chunks = <Array<number | Buffer>>bscript.decompile(script)
 
   if (chunks.length < 4) return false
   if (chunks[chunks.length - 1] !== OPS.OP_CHECKMULTISIG) return false
diff --git a/src/templates/pubkey/input.ts b/src/templates/pubkey/input.ts
index f4b8bf7..f9245e4 100644
--- a/src/templates/pubkey/input.ts
+++ b/src/templates/pubkey/input.ts
@@ -3,7 +3,7 @@
 import * as bscript from '../../script'
 
 export function check (script: Buffer | Array<number | Buffer>): boolean {
-  const chunks = bscript.decompile(script)
+  const chunks = <Array<number | Buffer>>bscript.decompile(script)
 
   return chunks.length === 1 &&
     bscript.isCanonicalScriptSignature(<Buffer>chunks[0])
diff --git a/src/templates/pubkey/output.ts b/src/templates/pubkey/output.ts
index 2728f68..f60cc05 100644
--- a/src/templates/pubkey/output.ts
+++ b/src/templates/pubkey/output.ts
@@ -4,7 +4,7 @@ import * as bscript from '../../script'
 const OPS = require('bitcoin-ops')
 
 export function check (script: Buffer | Array<number | Buffer>): boolean {
-  const chunks = bscript.decompile(script)
+  const chunks = <Array<number | Buffer>>bscript.decompile(script)
 
   return chunks.length === 2 &&
     bscript.isCanonicalPubKey(<Buffer>chunks[0]) &&
diff --git a/src/templates/pubkeyhash/input.ts b/src/templates/pubkeyhash/input.ts
index ffdc929..f27f809 100644
--- a/src/templates/pubkeyhash/input.ts
+++ b/src/templates/pubkeyhash/input.ts
@@ -3,7 +3,7 @@
 import * as bscript from '../../script'
 
 export function check (script: Buffer | Array<number | Buffer>): boolean {
-  const chunks = bscript.decompile(script)
+  const chunks = <Array<number | Buffer>>bscript.decompile(script)
 
   return chunks.length === 2 &&
     bscript.isCanonicalScriptSignature(<Buffer>chunks[0]) &&
diff --git a/src/templates/scripthash/input.ts b/src/templates/scripthash/input.ts
index 908a87b..93e7d58 100644
--- a/src/templates/scripthash/input.ts
+++ b/src/templates/scripthash/input.ts
@@ -10,13 +10,13 @@ import * as p2wsho from '../witnessscripthash/output'
 const Buffer = require('safe-buffer').Buffer
 
 export function check (script: Buffer | Array<number | Buffer>, allowIncomplete?: boolean): boolean {
-  const chunks = bscript.decompile(script)
+  const chunks = <Array<number | Buffer>>bscript.decompile(script)
   if (chunks.length < 1) return false
 
   const lastChunk = chunks[chunks.length - 1]
   if (!Buffer.isBuffer(lastChunk)) return false
 
-  const scriptSigChunks = bscript.decompile(bscript.compile(chunks.slice(0, -1)))
+  const scriptSigChunks = <Array<number | Buffer>>bscript.decompile(bscript.compile(chunks.slice(0, -1)))
   const redeemScriptChunks = bscript.decompile(<Buffer>lastChunk)
 
   // is redeemScript a valid script?
diff --git a/src/templates/witnesscommitment/output.ts b/src/templates/witnesscommitment/output.ts
index 1b3a182..d89b8e2 100644
--- a/src/templates/witnesscommitment/output.ts
+++ b/src/templates/witnesscommitment/output.ts
@@ -32,5 +32,5 @@ export function encode (commitment: Buffer): Buffer {
 export function decode (buffer: Buffer): Buffer {
   typeforce(check, buffer)
 
-  return (<Buffer>bscript.decompile(buffer)[1]).slice(4, 36)
+  return (<Buffer>(<Array<number | Buffer>>bscript.decompile(buffer))[1]).slice(4, 36)
 }
diff --git a/src/templates/witnesspubkeyhash/input.ts b/src/templates/witnesspubkeyhash/input.ts
index 36f0606..91b8357 100644
--- a/src/templates/witnesspubkeyhash/input.ts
+++ b/src/templates/witnesspubkeyhash/input.ts
@@ -7,7 +7,7 @@ function isCompressedCanonicalPubKey (pubKey: Buffer): boolean {
 }
 
 export function check (script: Buffer | Array<number | Buffer>): boolean {
-  const chunks = bscript.decompile(script)
+  const chunks = <Array<number | Buffer>>bscript.decompile(script)
 
   return chunks.length === 2 &&
     bscript.isCanonicalScriptSignature(<Buffer>chunks[0]) &&
diff --git a/src/transaction.ts b/src/transaction.ts
index 91956c5..af17449 100644
--- a/src/transaction.ts
+++ b/src/transaction.ts
@@ -182,7 +182,7 @@ export class Transaction {
     return this.ins.length === 1 && Transaction.isCoinbaseHash(this.ins[0].hash)
   }
 
-  addInput (hash: Buffer, index: number, sequence: number, scriptSig: Buffer): number {
+  addInput (hash: Buffer, index: number, sequence?: number, scriptSig?: Buffer): number {
     typeforce(types.tuple(
       types.Hash256bit,
       types.UInt32,
@@ -199,7 +199,7 @@ export class Transaction {
       hash: hash,
       index: index,
       script: scriptSig || EMPTY_SCRIPT,
-      sequence: sequence,
+      sequence: <number>sequence,
       witness: EMPTY_WITNESS
     }) - 1)
   }
@@ -293,7 +293,7 @@ export class Transaction {
     if (inIndex >= this.ins.length) return ONE
 
     // ignore OP_CODESEPARATOR
-    const ourScript = bscript.compile(bscript.decompile(prevOutScript).filter((x) => {
+    const ourScript = bscript.compile((<Array<Buffer | number>>bscript.decompile(prevOutScript)).filter((x) => {
       return x !== <number>opcodes.OP_CODESEPARATOR
     }))
 
@@ -475,7 +475,7 @@ export class Transaction {
     let offset = initialOffset || 0
 
     function writeSlice (slice: Buffer): void {
-      offset += slice.copy(buffer, offset)
+      offset += slice.copy(<Buffer>buffer, offset)
     }
 
     function writeUInt8 (i: number) {
diff --git a/src/transaction_builder.ts b/src/transaction_builder.ts
index e4c9c09..41d524e 100644
--- a/src/transaction_builder.ts
+++ b/src/transaction_builder.ts
@@ -24,8 +24,8 @@ interface TxbInput {
   redeemScript?: Buffer
   redeemScriptType?: string
   prevOutType?: string
-  pubkeys?: Array<Buffer>
-  signatures?: Array<Buffer>
+  pubkeys?: Array<Buffer> | Array<undefined>
+  signatures?: Array<Buffer> | Array<Buffer | undefined>
   witness?: Array<Buffer>
   witnessScript?: Buffer
   witnessScriptType?: string
@@ -38,7 +38,7 @@ interface TxbInput {
 interface TxbOutput {
   type: string
   pubkeys?: Array<Buffer>
-  signatures?: Array<Buffer>
+  signatures?: Array<Buffer> | Array<Buffer | undefined>
   maxSignatures?: number
 }
 
@@ -57,7 +57,7 @@ export class TransactionBuilder {
   private __inputs: Array<TxbInput>
   private __tx: Transaction
 
-  constructor (network: Network, maximumFeeRate?: number) {
+  constructor (network?: Network, maximumFeeRate?: number) {
     this.__prevTxSet = {}
     this.network = network || networks.bitcoin
 
@@ -125,7 +125,7 @@ export class TransactionBuilder {
       throw new Error('No, this would invalidate signatures')
     }
 
-    let value: number
+    let value: number | undefined = undefined
 
     // is it a hex string?
     if (txIsString(txHash)) {
@@ -225,7 +225,7 @@ export class TransactionBuilder {
     this.__inputs.forEach((input, i) => {
       if (!input.prevOutType && !allowIncomplete) throw new Error('Transaction is not complete')
 
-      const result = build(input.prevOutType, input, allowIncomplete)
+      const result = build(<string>input.prevOutType, input, allowIncomplete)
       if (!result) {
         if (!allowIncomplete && input.prevOutType === SCRIPT_TYPES.NONSTANDARD) throw new Error('Unknown input type')
         if (!allowIncomplete) throw new Error('Not enough information')
@@ -263,7 +263,7 @@ export class TransactionBuilder {
       throw new Error('Inconsistent redeemScript')
     }
 
-    const ourPubKey = keyPair.publicKey || keyPair.getPublicKey()
+    const ourPubKey = keyPair.publicKey || (<()=>Buffer>keyPair.getPublicKey)()
     if (!canSign(input)) {
       if (witnessValue !== undefined) {
         if (input.value !== undefined && input.value !== witnessValue) throw new Error('Input didn\'t match witnessValue')
@@ -284,15 +284,15 @@ export class TransactionBuilder {
     // ready to sign
     let signatureHash: Buffer
     if (input.hasWitness) {
-      signatureHash = this.__tx.hashForWitnessV0(vin, input.signScript, input.value, hashType)
+      signatureHash = this.__tx.hashForWitnessV0(vin, <Buffer>input.signScript, <number>input.value, hashType)
     } else {
-      signatureHash = this.__tx.hashForSignature(vin, input.signScript, hashType)
+      signatureHash = this.__tx.hashForSignature(vin, <Buffer>input.signScript, hashType)
     }
 
     // enforce in order signing of public keys
-    const signed = input.pubkeys.some((pubKey, i) => {
+    const signed = (<Array<Buffer>>input.pubkeys).some((pubKey, i) => {
       if (!ourPubKey.equals(pubKey)) return false
-      if (input.signatures[i]) throw new Error('Signature already exists')
+      if ((<Array<Buffer>>input.signatures)[i]) throw new Error('Signature already exists')
 
       // TODO: add tests
       if (ourPubKey.length !== 33 && input.hasWitness) {
@@ -300,7 +300,7 @@ export class TransactionBuilder {
       }
 
       const signature = keyPair.sign(signatureHash)
-      input.signatures[i] = bscript.signature.encode(signature, hashType)
+      ;(<Array<Buffer>>input.signatures)[i] = bscript.signature.encode(signature, hashType)
       return true
     })
 
@@ -348,7 +348,7 @@ export class TransactionBuilder {
     return this.__inputs.every(input => {
       if (input.signatures === undefined) return true
 
-      return input.signatures.every(signature => {
+      return input.signatures.every(<(signature: Buffer | undefined)=>boolean>(signature => {
         if (!signature) return true
         const hashType = signatureHashType(signature)
 
@@ -360,13 +360,13 @@ export class TransactionBuilder {
           // of more outputs
           return nInputs <= nOutputs
         }
-      })
+      }))
     })
   }
 
   private __overMaximumFees (bytes: number): boolean {
     // not all inputs will have .value defined
-    const incoming = this.__inputs.reduce((a, x) => a + (x.value >>> 0), 0)
+    const incoming = this.__inputs.reduce((a, x) => a + (<number>x.value >>> 0), 0)
 
     // but all outputs do, and if we have any input value
     // we can immediately determine if the outputs are too small
@@ -493,13 +493,13 @@ function expandInput (scriptSig: Buffer, witnessStack: Array<Buffer>, type?: str
 // could be done in expandInput, but requires the original Transaction for hashForSignature
 function fixMultisigOrder (input: TxbInput, transaction: Transaction, vin: number): void {
   if (input.redeemScriptType !== SCRIPT_TYPES.P2MS || !input.redeemScript) return
-  if (input.pubkeys.length === input.signatures.length) return
+  if ((<Array<Buffer>>input.pubkeys).length === (<Array<Buffer>>input.signatures).length) return
 
-  const unmatched = input.signatures.concat()
+  const unmatched = (<Array<Buffer | undefined>>input.signatures).concat()
 
-  input.signatures = input.pubkeys.map(pubKey => {
+  input.signatures = <Array<Buffer | undefined>>(<Array<Buffer>>input.pubkeys).map(pubKey => {
     const keyPair = ECPair.fromPublicKey(pubKey)
-    let match
+    let match: Buffer | undefined
 
     // check for a signature
     unmatched.some((signature, i) => {
@@ -508,7 +508,7 @@ function fixMultisigOrder (input: TxbInput, transaction: Transaction, vin: numbe
 
       // TODO: avoid O(n) hashForSignature
       const parsed = bscript.signature.decode(signature)
-      const hash = transaction.hashForSignature(vin, input.redeemScript, parsed.hashType)
+      const hash = transaction.hashForSignature(vin, (<Buffer>input.redeemScript), parsed.hashType)
 
       // skip if signature does not match pubKey
       if (!keyPair.verify(hash, parsed.signature)) return false
@@ -740,7 +740,7 @@ function prepareInput (input: TxbInput, ourPubKey: Buffer, redeemScript: Buffer,
   }
 }
 
-function build (type: string, input: TxbInput, allowIncomplete: boolean): any { //TODO payment type
+function build (type: string, input: TxbInput, allowIncomplete?: boolean): any { //TODO payment type
   const pubkeys = input.pubkeys || []
   let signatures = input.signatures || []
 
@@ -777,7 +777,7 @@ function build (type: string, input: TxbInput, allowIncomplete: boolean): any {
       return payments.p2ms({ m, pubkeys, signatures }, { allowIncomplete, validate })
     }
     case SCRIPT_TYPES.P2SH: {
-      const redeem = build(input.redeemScriptType, input, allowIncomplete)
+      const redeem = build(<string>input.redeemScriptType, input, allowIncomplete)
       if (!redeem) return
 
       return payments.p2sh({
@@ -789,7 +789,7 @@ function build (type: string, input: TxbInput, allowIncomplete: boolean): any {
       })
     }
     case SCRIPT_TYPES.P2WSH: {
-      const redeem = build(input.witnessScriptType, input, allowIncomplete)
+      const redeem = build(<string>input.witnessScriptType, input, allowIncomplete)
       if (!redeem) return
 
       return payments.p2wsh({
diff --git a/tsconfig.json b/tsconfig.json
index f8bd5e2..cfc286a 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -10,12 +10,12 @@
     "allowJs": false,
     "strict": false,
     "noImplicitAny": true,
-    "strictNullChecks": false,
+    "strictNullChecks": true,
     "strictFunctionTypes": true,
     "strictBindCallApply": true,
     "strictPropertyInitialization": false,
-    "noImplicitThis": false,
-    "alwaysStrict": false,
+    "noImplicitThis": true,
+    "alwaysStrict": true,
     "esModuleInterop": true
   },
   "include": [