diff --git a/README.md b/README.md
index 4da3c34..8b45781 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ All methods should be considered as expensive as they may need to do computation
 #### `source`
 
 ``` js
-Source.prototype.source() -> String
+Source.prototype.source() -> String | ArrayBuffer
 ```
 
 Returns the represented source code as string.
diff --git a/lib/CachedSource.js b/lib/CachedSource.js
index 940c4d9..08ca510 100644
--- a/lib/CachedSource.js
+++ b/lib/CachedSource.js
@@ -30,8 +30,10 @@ class CachedSource extends Source {
 
 	size() {
 		if(typeof this._cachedSize !== "undefined") return this._cachedSize;
-		if(typeof this._cachedSource !== "undefined")
-			return this._cachedSize = this._cachedSource.length;
+		if(typeof this._cachedSource !== "undefined") {
+			if(Buffer.from.length === 1) return new Buffer(this._cachedSource).length;
+			return this._cachedSize = Buffer.byteLength(this._cachedSource);
+		}
 		return this._cachedSize = this._source.size();
 	}
 
diff --git a/lib/Source.js b/lib/Source.js
index dccf737..f9b8f6b 100644
--- a/lib/Source.js
+++ b/lib/Source.js
@@ -14,7 +14,8 @@ class Source {
 	}
 
 	size() {
-		return this.source().length;
+		if(Buffer.from.length === 1) return new Buffer(this.source()).length;
+		return Buffer.byteLength(this.source())
 	}
 
 	map(options) {
diff --git a/test/CachedSource.js b/test/CachedSource.js
new file mode 100644
index 0000000..a622a0c
--- /dev/null
+++ b/test/CachedSource.js
@@ -0,0 +1,56 @@
+var should = require("should");
+var CachedSource = require("../lib/CachedSource");
+var OriginalSource = require('../lib/OriginalSource');
+
+describe("CachedSource", function() {
+	it("should return the correct size for binary files", function() {
+		var source = new OriginalSource(new ArrayBuffer(256), "file.wasm");
+		var cachedSource = new CachedSource(source);
+
+		cachedSource.size().should.be.eql(256);
+		cachedSource.size().should.be.eql(256);
+	});
+
+	it("should return the correct size for cached binary sources", function() {
+		var source = new OriginalSource(new ArrayBuffer(256), "file.wasm");
+		var cachedSource = new CachedSource(source);
+
+		cachedSource.source();
+		cachedSource.size().should.be.eql(256);
+		cachedSource.size().should.be.eql(256);
+	});
+
+	it("should return the correct size for text files", function() {
+		var source = new OriginalSource("TestTestTest", "file.js");
+		var cachedSource = new CachedSource(source);
+
+		cachedSource.size().should.be.eql(12);
+		cachedSource.size().should.be.eql(12);
+	});
+
+	it("should return the correct size for cached text files", function() {
+		var source = new OriginalSource("TestTestTest", "file.js");
+		var cachedSource = new CachedSource(source);
+
+		cachedSource.source();
+		cachedSource.size().should.be.eql(12);
+		cachedSource.size().should.be.eql(12);
+	});
+
+	it("should return the correct size for unicode files", function() {
+		var source = new OriginalSource("😋", "file.js");
+		var cachedSource = new CachedSource(source);
+
+		cachedSource.size().should.be.eql(4);
+		cachedSource.size().should.be.eql(4);
+	});
+
+	it("should return the correct size for cached unicode files", function() {
+		var source = new OriginalSource("😋", "file.js");
+		var cachedSource = new CachedSource(source);
+
+		cachedSource.source();
+		cachedSource.size().should.be.eql(4);
+		cachedSource.size().should.be.eql(4);
+	});
+});
diff --git a/test/OriginalSource.js b/test/OriginalSource.js
index 9e2a591..08ecf47 100644
--- a/test/OriginalSource.js
+++ b/test/OriginalSource.js
@@ -56,4 +56,14 @@ describe("OriginalSource", function() {
 
 		resultMap.mappings.should.be.eql("AAAA;AACA;AACA");
 	});
+
+	it("should return the correct size for binary files", function() {
+		var source = new OriginalSource(new ArrayBuffer(256), "file.wasm");
+		source.size().should.be.eql(256);
+	});
+
+	it("should return the correct size for unicode files", function() {
+		var source = new OriginalSource("😋", "file.js");
+		source.size().should.be.eql(4);
+	});
 });