diff --git a/README.md b/README.md
index 2e4cb3c..b6a5c2f 100644
--- a/README.md
+++ b/README.md
@@ -66,6 +66,34 @@ unflatten({
 
 Use a custom delimiter for (un)flattening your objects, instead of `.`.
 
+### keyname
+
+Use a custom `function` to flatten the keyname.  By default, the `delimiter` is inserted between `prev` and `next`
+
+Here's an example that uses a colon (':') to prefix and delimit the keyname
+
+````javascript
+var o = {
+  hello: {
+    world: {
+      again: 'good morning'
+}}}
+
+flatten(o, { keyname: function(prev, next) {
+  return prev 
+    ? prev + ':' + next 
+    : ':' + next
+}})
+      
+// {
+//  ':hello:world:again': 'good morning'
+// }
+````
+
+### keynames
+
+Use a custom `function` to unflatten the keyname.  It  returns an array of key names.  This is the inverse of [keyname](#keyname). By default, the `delimiter` is used to [split](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split) the name.
+
 ### safe
 
 When enabled, both `flat` and `unflatten` will preserve arrays and their
diff --git a/index.js b/index.js
index e22351e..87399b3 100644
--- a/index.js
+++ b/index.js
@@ -9,6 +9,14 @@ function flatten(target, opts) {
 
   var delimiter = opts.delimiter || '.'
   var maxDepth = opts.maxDepth
+
+  function flattenKeyname(prev, key) {
+    return prev
+      ? prev + delimiter + key
+      : key
+  }
+
+  var keyname = opts.keyname || flattenKeyname;
   var output = {}
 
   function step(object, prev, currentDepth) {
@@ -23,9 +31,7 @@ function flatten(target, opts) {
         type === "[object Array]"
       )
 
-      var newKey = prev
-        ? prev + delimiter + key
-        : key
+      var newKey = keyname(prev, key)
 
       if (!isarray && !isbuffer && isobject && Object.keys(value).length &&
         (!opts.maxDepth || currentDepth < maxDepth)) {
@@ -53,6 +59,12 @@ function unflatten(target, opts) {
     return target
   }
 
+  function unflattenKeyname(key) {
+    return key.split(delimiter)
+  }
+
+  var keynames = opts.keynames || unflattenKeyname;
+
   // safely ensure that the key is
   // an integer.
   function getkey(key) {
@@ -66,7 +78,7 @@ function unflatten(target, opts) {
   }
 
   Object.keys(target).forEach(function(key) {
-    var split = key.split(delimiter)
+    var split = keynames(key)
     var key1 = getkey(split.shift())
     var key2 = getkey(split[0])
     var recipient = result
diff --git a/test/test.js b/test/test.js
index 1261921..fdceedb 100644
--- a/test/test.js
+++ b/test/test.js
@@ -103,6 +103,22 @@ suite('Flatten', function() {
     })
   })
 
+  test('Custom keyname', function() {
+    assert.deepEqual(flatten({
+      hello: {
+        world: {
+          again: 'good morning'
+        }
+      }
+    }, {
+      keyname: function(prev, key) {
+        return prev ? prev + ':' + key : ':' + key
+      }
+    }), {
+      ':hello:world:again': 'good morning'
+    })
+  })
+
   test('Empty Objects', function() {
     assert.deepEqual(flatten({
       hello: {
@@ -223,6 +239,22 @@ suite('Unflatten', function() {
     }))
   })
 
+  test('Custom keynames', function() {
+    assert.deepEqual({
+      hello: {
+        world: {
+          again: 'good morning'
+        }
+      }
+    }, unflatten({
+      ':hello:world:again': 'good morning'
+    }, {
+      keynames: function(key) {
+        return key.substr(1).split(':')
+      }
+    }))
+  })
+
   test('Overwrite', function() {
     assert.deepEqual({
       travis: {