diff --git a/src/memoizerific.js b/src/memoizerific.js
index fcf34e9..b6115b2 100644
--- a/src/memoizerific.js
+++ b/src/memoizerific.js
@@ -1,9 +1,13 @@
 var MapOrSimilar = require('map-or-similar');
 
-module.exports = function (limit) {
+module.exports = function (limit, normalizerFn) {
 	var cache = new MapOrSimilar(process.env.FORCE_SIMILAR_INSTEAD_OF_MAP === 'true'),
 		lru = [];
 
+  if (normalizerFn === undefined) {
+    normalizerFn = function (obj) { return obj; };
+  }
+
 	return function (fn) {
 		var memoizerific = function () {
 			var currentCache = cache,
@@ -20,15 +24,16 @@ module.exports = function (limit) {
 
 			// loop through each argument to traverse the map tree
 			for (i = 0; i < argsLengthMinusOne; i++) {
+				var key = normalizerFn(arguments[i]);
 				lruPath[i] = {
 					cacheItem: currentCache,
-					arg: arguments[i]
+					arg: key
 				};
 
 				// climb through the hierarchical map tree until the second-last argument has been found, or an argument is missing.
 				// if all arguments up to the second-last have been found, this will potentially be a cache hit (determined later)
-				if (currentCache.has(arguments[i])) {
-					currentCache = currentCache.get(arguments[i]);
+				if (currentCache.has(key)) {
+					currentCache = currentCache.get(key);
 					continue;
 				}
 
@@ -36,14 +41,15 @@ module.exports = function (limit) {
 
 				// make maps until last value
 				newMap = new MapOrSimilar(process.env.FORCE_SIMILAR_INSTEAD_OF_MAP === 'true');
-				currentCache.set(arguments[i], newMap);
+				currentCache.set(key, newMap);
 				currentCache = newMap;
 			}
 
+			var key = normalizerFn(arguments[argsLengthMinusOne]);
 			// we are at the last arg, check if it is really memoized
 			if (isMemoized) {
-				if (currentCache.has(arguments[argsLengthMinusOne])) {
-					fnResult = currentCache.get(arguments[argsLengthMinusOne]);
+				if (currentCache.has(key)) {
+					fnResult = currentCache.get(key);
 				}
 				else {
 					isMemoized = false;
@@ -53,14 +59,14 @@ module.exports = function (limit) {
 			// if the result wasn't memoized, compute it and cache it
 			if (!isMemoized) {
 				fnResult = fn.apply(null, arguments);
-				currentCache.set(arguments[argsLengthMinusOne], fnResult);
+				currentCache.set(key, fnResult);
 			}
 
 			// if there is a cache limit, purge any extra results
 			if (limit > 0) {
 				lruPath[argsLengthMinusOne] = {
 					cacheItem: currentCache,
-					arg: arguments[argsLengthMinusOne]
+					arg: key
 				};
 
 				if (isMemoized) {
@@ -138,4 +144,4 @@ function removeCachedResult(removedLru) {
 // check if the numbers are equal, or whether they are both precisely NaN (isNaN returns true for all non-numbers)
 function isEqual(val1, val2) {
 	return val1 === val2 || (val1 !== val1 && val2 !== val2);
-}
\ No newline at end of file
+}
diff --git a/tests/custom-normalizer.js b/tests/custom-normalizer.js
new file mode 100644
index 0000000..76d3cd5
--- /dev/null
+++ b/tests/custom-normalizer.js
@@ -0,0 +1,35 @@
+var Memoizerific = require('../src/memoizerific');
+
+describe("null args", () => {
+	var memoizedFn,
+		arg1 = null,
+		arg2 = undefined,
+		arg3 = NaN; // important to test since NaN does not equal NaN
+
+	beforeEach(function() {
+		memoizedFn = Memoizerific(50)(function(arg1, arg2, arg3) {
+			return '';
+		});
+		memoizedFn(arg1, arg2, arg3);
+	});
+
+	it("should be map or similar", () => { expect(memoizedFn.cache instanceof Map).toEqual(process.env.FORCE_SIMILAR_INSTEAD_OF_MAP !== 'true'); });
+
+	it("should not be memoized", () => {
+		expect(memoizedFn.wasMemoized).toEqual(false);
+		expect(memoizedFn.lru.length).toEqual(1);
+	});
+
+	it("should be memoized", () => {
+		memoizedFn(arg1, arg2, arg3);
+		expect(memoizedFn.wasMemoized).toEqual(true);
+		expect(memoizedFn.lru.length).toEqual(1);
+	});
+
+	it("should have multiple cached items", () => {
+		memoizedFn(arg1, arg2, arg3);
+		memoizedFn(arg1, arg2, 1);
+		expect(memoizedFn.wasMemoized).toEqual(false);
+		expect(memoizedFn.lru.length).toEqual(2);
+	});
+});
diff --git a/tests/null-args.js b/tests/null-args.js
index 76d3cd5..bb4cb5e 100644
--- a/tests/null-args.js
+++ b/tests/null-args.js
@@ -1,35 +1,34 @@
 var Memoizerific = require('../src/memoizerific');
 
-describe("null args", () => {
-	var memoizedFn,
-		arg1 = null,
-		arg2 = undefined,
-		arg3 = NaN; // important to test since NaN does not equal NaN
-
-	beforeEach(function() {
-		memoizedFn = Memoizerific(50)(function(arg1, arg2, arg3) {
-			return '';
-		});
-		memoizedFn(arg1, arg2, arg3);
-	});
+describe("custom normalizer", () => {
+	var memoizedFn;
 
-	it("should be map or similar", () => { expect(memoizedFn.cache instanceof Map).toEqual(process.env.FORCE_SIMILAR_INSTEAD_OF_MAP !== 'true'); });
+	it("should always be memoized", () => {
+    var memoizedFn =
+      Memoizerific(100, function () { return true; })
+      (function (obj) { return obj; });
 
-	it("should not be memoized", () => {
-		expect(memoizedFn.wasMemoized).toEqual(false);
-		expect(memoizedFn.lru.length).toEqual(1);
-	});
+    memoizedFn({a: 1});
 
-	it("should be memoized", () => {
-		memoizedFn(arg1, arg2, arg3);
+    memoizedFn(1);
+		expect(memoizedFn.wasMemoized).toEqual(true);
+    memoizedFn([1, 2, 3]);
 		expect(memoizedFn.wasMemoized).toEqual(true);
-		expect(memoizedFn.lru.length).toEqual(1);
 	});
 
-	it("should have multiple cached items", () => {
-		memoizedFn(arg1, arg2, arg3);
-		memoizedFn(arg1, arg2, 1);
+	it("should be memoized based on custom function", () => {
+    var memoizedFn =
+      Memoizerific(100, function (i) { return i % 2; })
+      (function (obj) { return obj; });
+
+    memoizedFn(1);
+    memoizedFn(3);
+		expect(memoizedFn.wasMemoized).toEqual(true);
+
+    memoizedFn(2);
 		expect(memoizedFn.wasMemoized).toEqual(false);
-		expect(memoizedFn.lru.length).toEqual(2);
+
+    memoizedFn(4);
+		expect(memoizedFn.wasMemoized).toEqual(true);
 	});
 });