diff --git a/.gitignore b/.gitignore
index c3c6b061..3da8ee83 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 docs
 package-lock.json
 yarn.lock
+.nyc_output
 
 # Logs
 logs
diff --git a/README.md b/README.md
index 5e7a445a..0b111b4f 100644
--- a/README.md
+++ b/README.md
@@ -36,6 +36,7 @@ The UnixFS spec can be found inside the [ipfs/specs repository](http://github.co
     - [get total fileSize](#get-total-filesize)
     - [marshal and unmarshal](#marshal-and-unmarshal)
     - [is this UnixFS entry a directory?](#is-this-unixfs-entry-a-directory)
+    - [has an mtime been set?](#has-an-mtime-been-set)
 - [Contribute](#contribute)
 - [License](#license)
 
@@ -116,7 +117,12 @@ message Data {
   optional uint64 hashType = 5;
   optional uint64 fanout = 6;
   optional uint32 mode = 7;
-  optional int64 mtime = 8;
+  optional UnixTime mtime = 8;
+}
+
+message UnixTime {
+  required int64 Seconds = 1;
+  optional fixed32 FractionalNanoseconds = 2;
 }
 
 message Metadata {
@@ -142,7 +148,7 @@ const data = new UnixFS([options])
 - data (Buffer): The optional data field for this node
 - blockSizes (Array, default: `[]`): If this is a `file` node that is made up of multiple blocks, `blockSizes` is a list numbers that represent the size of the file chunks stored in each child node. It is used to calculate the total file size.
 - mode (Number, default `0644` for files, `0755` for directories/hamt-sharded-directories) file mode
-- mtime (Date, default `0`): The modification time of this node
+- mtime (Date, { secs, nsecs }, { Seconds, FractionalNanoseconds }, [ secs, nsecs ], default { secs: 0 }): The modification time of this node
 
 #### add and remove a block size to the block size list
 
@@ -177,6 +183,20 @@ const file = new Data({ type: 'file' })
 file.isDirectory() // false
 ```
 
+#### has an mtime been set?
+
+If no modification time has been set, no `mtime` property will be present on the `Data` instance:
+
+```JavaScript
+const file = new Data({ type: 'file' })
+file.mtime // undefined
+
+Object.prototype.hasOwnProperty.call(file, 'mtime') // false
+
+const dir = new Data({ type: 'dir', mtime: new Date() })
+dir.mtime // { secs: Number, nsecs: Number }
+```
+
 ## Contribute
 
 Feel free to join in. All welcome. Open an [issue](https://github.com/ipfs/js-ipfs-unixfs/issues)!
diff --git a/package.json b/package.json
index f00d3084..c9c3551e 100644
--- a/package.json
+++ b/package.json
@@ -17,7 +17,7 @@
     "release": "aegir release",
     "release-minor": "aegir release --type minor",
     "release-major": "aegir release --type major",
-    "coverage": "aegir coverage"
+    "coverage": "nyc -s aegir test -t node && nyc report --reporter=html"
   },
   "repository": {
     "type": "git",
@@ -38,9 +38,11 @@
   "devDependencies": {
     "aegir": "^20.4.1",
     "chai": "^4.2.0",
-    "dirty-chai": "^2.0.1"
+    "dirty-chai": "^2.0.1",
+    "nyc": "^15.0.0"
   },
   "dependencies": {
+    "err-code": "^2.0.0",
     "protons": "^1.1.0"
   },
   "contributors": [
diff --git a/src/index.js b/src/index.js
index 6331bdc1..5f77a9c1 100644
--- a/src/index.js
+++ b/src/index.js
@@ -3,6 +3,7 @@
 const protons = require('protons')
 const pb = protons(require('./unixfs.proto'))
 const unixfsData = pb.Data
+const errcode = require('err-code')
 
 const types = [
   'raw',
@@ -45,6 +46,84 @@ function parseArgs (args) {
   return args[0]
 }
 
+function parseMtime (mtime) {
+  if (mtime == null) {
+    return undefined
+  }
+
+  // { secs, nsecs }
+  if (Object.prototype.hasOwnProperty.call(mtime, 'secs')) {
+    mtime = {
+      secs: mtime.secs,
+      nsecs: mtime.nsecs
+    }
+  }
+
+  // UnixFS TimeSpec
+  if (Object.prototype.hasOwnProperty.call(mtime, 'Seconds')) {
+    mtime = {
+      secs: mtime.Seconds,
+      nsecs: mtime.FractionalNanoseconds
+    }
+  }
+
+  // process.hrtime()
+  if (Array.isArray(mtime)) {
+    mtime = {
+      secs: mtime[0],
+      nsecs: mtime[1]
+    }
+  }
+
+  // Javascript Date
+  if (mtime instanceof Date) {
+    const ms = mtime.getTime()
+    const secs = Math.floor(ms / 1000)
+
+    mtime = {
+      secs: secs,
+      nsecs: (ms - (secs * 1000)) * 1000
+    }
+  }
+
+  /*
+  TODO: https://github.com/ipfs/aegir/issues/487
+
+  // process.hrtime.bigint()
+  if (typeof mtime === 'bigint') {
+    const secs = mtime / BigInt(1e9)
+    const nsecs = mtime - (secs * BigInt(1e9))
+
+    mtime = {
+      secs: parseInt(secs),
+      nsecs: parseInt(nsecs)
+    }
+  }
+  */
+
+  if (!Object.prototype.hasOwnProperty.call(mtime, 'secs')) {
+    return undefined
+  }
+
+  if (mtime.nsecs < 0 || mtime.nsecs > 999999999) {
+    throw errcode(new Error('mtime-nsecs must be within the range [0,999999999]'), 'ERR_INVALID_MTIME_NSECS')
+  }
+
+  return mtime
+}
+
+function parseMode (mode) {
+  if (mode == null) {
+    return undefined
+  }
+
+  if (typeof mode === 'string' || mode instanceof String) {
+    mode = parseInt(mode, 8)
+  }
+
+  return mode & 0xFFF
+}
+
 class Data {
   // decode from protobuf https://github.com/ipfs/specs/blob/master/UNIXFS.md
   static unmarshal (marshaled) {
@@ -55,7 +134,7 @@ class Data {
       data: decoded.hasData() ? decoded.Data : undefined,
       blockSizes: decoded.blocksizes,
       mode: decoded.hasMode() ? decoded.mode : undefined,
-      mtime: decoded.hasMtime() ? new Date(decoded.mtime * 1000) : undefined
+      mtime: decoded.hasMtime() ? decoded.mtime : undefined
     })
   }
 
@@ -71,7 +150,7 @@ class Data {
     } = parseArgs(args)
 
     if (!types.includes(type)) {
-      throw new Error('Type: ' + type + ' is not valid')
+      throw errcode(new Error('Type: ' + type + ' is not valid'), 'ERR_INVALID_TYPE')
     }
 
     this.type = type
@@ -79,10 +158,14 @@ class Data {
     this.hashType = hashType
     this.fanout = fanout
     this.blockSizes = blockSizes || []
-    this.mtime = mtime || new Date(0)
-    this.mode = mode || mode === 0 ? (mode & 0xFFF) : undefined
     this._originalMode = mode
 
+    const parsedMode = parseMode(mode)
+
+    if (parsedMode !== undefined) {
+      this.mode = parsedMode
+    }
+
     if (this.mode === undefined && type === 'file') {
       this.mode = DEFAULT_FILE_MODE
     }
@@ -90,6 +173,12 @@ class Data {
     if (this.mode === undefined && this.isDirectory()) {
       this.mode = DEFAULT_DIRECTORY_MODE
     }
+
+    const parsedMtime = parseMtime(mtime)
+
+    if (parsedMtime) {
+      this.mtime = parsedMtime
+    }
   }
 
   isDirectory () {
@@ -135,7 +224,7 @@ class Data {
       case 'symlink': type = unixfsData.DataType.Symlink; break
       case 'hamt-sharded-directory': type = unixfsData.DataType.HAMTShard; break
       default:
-        throw new Error(`Unkown type: "${this.type}"`)
+        throw errcode(new Error('Type: ' + type + ' is not valid'), 'ERR_INVALID_TYPE')
     }
 
     let data = this.data
@@ -152,8 +241,8 @@ class Data {
 
     let mode
 
-    if (this.mode || this.mode === 0) {
-      mode = (this._originalMode & 0xFFFFF000) | (this.mode & 0xFFF)
+    if (this.mode != null) {
+      mode = (this._originalMode & 0xFFFFF000) | parseMode(this.mode)
 
       if (mode === DEFAULT_FILE_MODE && this.type === 'file') {
         mode = undefined
@@ -166,11 +255,18 @@ class Data {
 
     let mtime
 
-    if (this.mtime) {
-      mtime = Math.round(this.mtime.getTime() / 1000)
+    if (this.mtime != null) {
+      const parsed = parseMtime(this.mtime)
+
+      if (parsed) {
+        mtime = {
+          Seconds: parsed.secs,
+          FractionalNanoseconds: parsed.nsecs
+        }
 
-      if (mtime === 0) {
-        mtime = undefined
+        if (mtime.FractionalNanoseconds === 0) {
+          delete mtime.FractionalNanoseconds
+        }
       }
     }
 
diff --git a/src/unixfs.proto.js b/src/unixfs.proto.js
index fcc8931d..5b6b3181 100644
--- a/src/unixfs.proto.js
+++ b/src/unixfs.proto.js
@@ -20,7 +20,12 @@ message Data {
   optional uint64 hashType = 5;
   optional uint64 fanout = 6;
   optional uint32 mode = 7;
-  optional int64 mtime = 8;
+  optional UnixTime mtime = 8;
+}
+
+message UnixTime {
+  required int64 Seconds = 1;
+  optional fixed32 FractionalNanoseconds = 2;
 }
 
 message Metadata {
diff --git a/test/unixfs-format.spec.js b/test/unixfs-format.spec.js
index 6190fbf4..e8bf137d 100644
--- a/test/unixfs-format.spec.js
+++ b/test/unixfs-format.spec.js
@@ -17,6 +17,20 @@ const protons = require('protons')
 const unixfsData = protons(require('../src/unixfs.proto')).Data
 
 describe('unixfs-format', () => {
+  it('old style constructor', () => {
+    const buf = Buffer.from('hello world')
+    const entry = new UnixFS('file', buf)
+
+    expect(entry.type).to.equal('file')
+    expect(entry.data).to.deep.equal(buf)
+  })
+
+  it('old style constructor with single argument', () => {
+    const entry = new UnixFS('file')
+
+    expect(entry.type).to.equal('file')
+  })
+
   it('defaults to file', () => {
     const data = new UnixFS()
     expect(data.type).to.equal('file')
@@ -116,6 +130,30 @@ describe('unixfs-format', () => {
     expect(UnixFS.unmarshal(data.marshal())).to.have.property('mode', mode)
   })
 
+  it('default mode for files', () => {
+    const data = new UnixFS({
+      type: 'file'
+    })
+
+    expect(UnixFS.unmarshal(data.marshal())).to.have.property('mode', parseInt('0644', 8))
+  })
+
+  it('default mode for directories', () => {
+    const data = new UnixFS({
+      type: 'directory'
+    })
+
+    expect(UnixFS.unmarshal(data.marshal())).to.have.property('mode', parseInt('0755', 8))
+  })
+
+  it('default mode for hamt shards', () => {
+    const data = new UnixFS({
+      type: 'hamt-sharded-directory'
+    })
+
+    expect(UnixFS.unmarshal(data.marshal())).to.have.property('mode', parseInt('0755', 8))
+  })
+
   it('sets mode to 0', () => {
     const mode = 0
     const data = new UnixFS({
@@ -126,8 +164,29 @@ describe('unixfs-format', () => {
     expect(UnixFS.unmarshal(data.marshal())).to.have.property('mode', mode)
   })
 
+  it('mode as string', () => {
+    const data = new UnixFS({
+      type: 'file',
+      mode: '0555'
+    })
+
+    expect(UnixFS.unmarshal(data.marshal())).to.have.property('mode', parseInt('0555', 8))
+  })
+
+  it('mode as string set outside constructor', () => {
+    const data = new UnixFS({
+      type: 'file'
+    })
+    data.mode = '0555'
+
+    expect(UnixFS.unmarshal(data.marshal())).to.have.property('mode', parseInt('0555', 8))
+  })
+
   it('mtime', () => {
-    const mtime = new Date()
+    const mtime = {
+      secs: 5,
+      nsecs: 0
+    }
     const data = new UnixFS({
       type: 'file',
       mtime
@@ -135,16 +194,127 @@ describe('unixfs-format', () => {
 
     const marshaled = data.marshal()
     const unmarshaled = UnixFS.unmarshal(marshaled)
-    expect(unmarshaled.mtime).to.deep.equal(new Date(Math.round(mtime.getTime() / 1000) * 1000))
+    expect(unmarshaled).to.have.deep.property('mtime', mtime)
+  })
+
+  it('default mtime', () => {
+    const data = new UnixFS({
+      type: 'file'
+    })
+
+    const marshaled = data.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.not.have.property('mtime')
   })
 
+  it('mtime as date', () => {
+    const mtime = {
+      secs: 5,
+      nsecs: 0
+    }
+    const data = new UnixFS({
+      type: 'file',
+      mtime: new Date(5000)
+    })
+
+    const marshaled = data.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.have.deep.property('mtime', mtime)
+  })
+
+  it('mtime as hrtime', () => {
+    const mtime = {
+      secs: 5,
+      nsecs: 0
+    }
+    const data = new UnixFS({
+      type: 'file',
+      mtime: [5, 0]
+    })
+
+    const marshaled = data.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.have.deep.property('mtime', mtime)
+  })
+  /*
+  TODO: https://github.com/ipfs/aegir/issues/487
+
+  it('mtime as bigint', () => {
+    const mtime = {
+      secs: 5,
+      nsecs: 0
+    }
+    const data = new UnixFS({
+      type: 'file',
+      mtime: BigInt(5 * 1e9)
+    })
+
+    const marshaled = data.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.have.deep.property('mtime', mtime)
+  })
+  */
   it('sets mtime to 0', () => {
-    const mtime = new Date(0)
+    const mtime = {
+      secs: 0,
+      nsecs: 0
+    }
     const data = new UnixFS({
       type: 'file',
       mtime
     })
-    expect(UnixFS.unmarshal(data.marshal())).to.have.deep.property('mtime', new Date(Math.round(mtime.getTime() / 1000) * 1000))
+
+    const marshaled = data.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.have.deep.property('mtime', mtime)
+  })
+
+  it('mtime as date set outside constructor', () => {
+    const mtime = {
+      secs: 5,
+      nsecs: 0
+    }
+    const data = new UnixFS({
+      type: 'file'
+    })
+    data.mtime = new Date(5000)
+
+    const marshaled = data.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.have.deep.property('mtime', mtime)
+  })
+
+  it('ignores invalid mtime', () => {
+    const data = new UnixFS({
+      type: 'file',
+      mtime: 'what is this'
+    })
+
+    const marshaled = data.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.not.have.property('mtime')
+  })
+
+  it('ignores invalid mtime set outside of constructor', () => {
+    const entry = new UnixFS({
+      type: 'file'
+    })
+    entry.mtime = 'what is this'
+
+    const marshaled = entry.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.not.have.property('mtime')
+  })
+
+  it('survives null mtime', () => {
+    const entry = new UnixFS({
+      type: 'file'
+    })
+    entry.mtime = null
+
+    const marshaled = entry.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+    expect(unmarshaled).to.not.have.property('mtime')
   })
 
   it('does not overwrite unknown mode bits', () => {
@@ -162,7 +332,16 @@ describe('unixfs-format', () => {
   })
 
   // figuring out what is this metadata for https://github.com/ipfs/js-ipfs-data-importing/issues/3#issuecomment-182336526
-  it.skip('metadata', () => {})
+  it('metadata', () => {
+    const entry = new UnixFS({
+      type: 'metadata'
+    })
+
+    const marshaled = entry.marshal()
+    const unmarshaled = UnixFS.unmarshal(marshaled)
+
+    expect(unmarshaled).to.have.property('type', 'metadata')
+  })
 
   it('symlink', () => {
     const data = new UnixFS({
@@ -175,15 +354,37 @@ describe('unixfs-format', () => {
     expect(data.blockSizes).to.deep.equal(unmarshaled.blockSizes)
     expect(data.fileSize()).to.deep.equal(unmarshaled.fileSize())
   })
-  it('wrong type', (done) => {
-    let data
+
+  it('invalid type', (done) => {
     try {
-      data = new UnixFS({
+      // eslint-disable-next-line no-new
+      new UnixFS({
         type: 'bananas'
       })
     } catch (err) {
-      expect(err).to.exist()
-      expect(data).to.not.exist()
+      expect(err).to.have.property('code', 'ERR_INVALID_TYPE')
+      done()
+    }
+  })
+
+  it('invalid type with old style constructor', (done) => {
+    try {
+      // eslint-disable-next-line no-new
+      new UnixFS('bananas')
+    } catch (err) {
+      expect(err).to.have.property('code', 'ERR_INVALID_TYPE')
+      done()
+    }
+  })
+
+  it('invalid type set outside constructor', (done) => {
+    const entry = new UnixFS()
+    entry.type = 'bananas'
+
+    try {
+      entry.marshal()
+    } catch (err) {
+      expect(err).to.have.property('code', 'ERR_INVALID_TYPE')
       done()
     }
   })