diff --git a/src/util.js b/src/util.js
index 290cbc8..dd9e8ec 100644
--- a/src/util.js
+++ b/src/util.js
@@ -69,7 +69,25 @@ exports.deserialize = (data, callback) => {
   }
 }
 
-exports.cid = (dagNode, callback) => {
+/**
+ * @callback CidCallback
+ * @param {?Error} error - Error if getting the CID failed
+ * @param {?CID} cid - CID if call was successful
+ */
+/**
+ * Get the CID of the DAG-Node.
+ *
+ * @param {Object} dagNode - Internal representation
+ * @param {Object} [options] - Ignored
+ * @param {CidCallback} callback - Callback that handles the return value
+ * @returns {void}
+ */
+exports.cid = (dagNode, options, callback) => {
+  if (typeof options === 'function') {
+    callback = options
+    options = {}
+  }
+  options = options || {}
   waterfall([
     (cb) => exports.serialize(dagNode, cb),
     (serialized, cb) => multihashing(serialized, resolver.defaultHashAlg, cb),
diff --git a/test/util.spec.js b/test/util.spec.js
new file mode 100644
index 0000000..8f70fd6
--- /dev/null
+++ b/test/util.spec.js
@@ -0,0 +1,61 @@
+/* eslint-env mocha */
+'use strict'
+
+const chai = require('chai')
+const dirtyChai = require('dirty-chai')
+const expect = chai.expect
+chai.use(dirtyChai)
+const ipldGit = require('../src')
+const multihash = require('multihashes')
+const CID = require('cids')
+
+describe('IPLD format util', () => {
+  const tagNode = {
+    gitType: 'tag',
+    object: {'/': new CID('z8mWaHQaEAKd5KMRNU3npB3saSZmhFh3e').buffer},
+    type: 'commit',
+    tag: 'v0.0.0',
+    tagger: {
+      name: 'John Doe',
+      email: 'johndoe@example.com',
+      date: '1497302532 +0200'
+    },
+    message: 'A message\n'
+  }
+
+  it('.serialize and .deserialize', (done) => {
+    ipldGit.util.serialize(tagNode, (err, serialized) => {
+      expect(err).to.not.exist()
+      expect(Buffer.isBuffer(serialized)).to.equal(true)
+      ipldGit.util.deserialize(serialized, (err, deserialized) => {
+        expect(err).to.not.exist()
+        expect(tagNode).to.eql(deserialized)
+        done()
+      })
+    })
+  })
+
+  it('.cid', (done) => {
+    ipldGit.util.cid(tagNode, (err, cid) => {
+      expect(err).to.not.exist()
+      expect(cid.version).to.equal(1)
+      expect(cid.codec).to.equal('git-raw')
+      expect(cid.multihash).to.exist()
+      const mh = multihash.decode(cid.multihash)
+      expect(mh.name).to.equal('sha1')
+      done()
+    })
+  })
+
+  it('.cid ignores options', (done) => {
+    ipldGit.util.cid(tagNode, { hashAlg: 'unknown' }, (err, cid) => {
+      expect(err).to.not.exist()
+      expect(cid.version).to.equal(1)
+      expect(cid.codec).to.equal('git-raw')
+      expect(cid.multihash).to.exist()
+      const mh = multihash.decode(cid.multihash)
+      expect(mh.name).to.equal('sha1')
+      done()
+    })
+  })
+})