diff --git a/index.d.ts b/index.d.ts
index ee8d420..87416d1 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,4 +1,4 @@
 declare module 'base64-arraybuffer' {
     export function encode(buffer: ArrayBuffer): string;
-    export function decode(str: string): ArrayBuffer;
+    export function decode(str: string, start?: number): ArrayBuffer;
 }
diff --git a/lib/base64-arraybuffer.js b/lib/base64-arraybuffer.js
index e6b6306..0cbf9a7 100644
--- a/lib/base64-arraybuffer.js
+++ b/lib/base64-arraybuffer.js
@@ -36,9 +36,13 @@
     return base64;
   };
 
-  exports.decode =  function(base64) {
-    var bufferLength = base64.length * 0.75,
-    len = base64.length, i, p = 0,
+  exports.decode =  function(base64, start) {
+    var len = base64.length
+    var i = 0;
+    if(start < len && start > 0) i = start;
+    else if(start > len) i = len;
+
+    var bufferLength = (len - i) * 0.75, p = 0,
     encoded1, encoded2, encoded3, encoded4;
 
     if (base64[base64.length - 1] === "=") {
@@ -51,7 +55,7 @@
     var arraybuffer = new ArrayBuffer(bufferLength),
     bytes = new Uint8Array(arraybuffer);
 
-    for (i = 0; i < len; i+=4) {
+    for (i; i < len; i+=4) {
       encoded1 = lookup[base64.charCodeAt(i)];
       encoded2 = lookup[base64.charCodeAt(i+1)];
       encoded3 = lookup[base64.charCodeAt(i+2)];
diff --git a/test/base64-arraybuffer_test.js b/test/base64-arraybuffer_test.js
index 76d22ae..5823d3f 100644
--- a/test/base64-arraybuffer_test.js
+++ b/test/base64-arraybuffer_test.js
@@ -52,5 +52,7 @@ describe('decode', () => {
   it('decode "Man"', () => ok(testArrayBuffers(decode("TWFu"), stringArrayBuffer("Man"))));
   it('decode "Hello world"', () => ok(testArrayBuffers(decode("SGVsbG8gd29ybGQ="), stringArrayBuffer("Hello world"))));
   it('decode "Hello worlds!"', () => ok(testArrayBuffers(decode("SGVsbG8gd29ybGRzIQ=="), stringArrayBuffer("Hello worlds!"))));
+  it('decode "Hello world" - discard start < 0', () => ok(testArrayBuffers(decode("SGVsbG8gd29ybGQ=", -1), stringArrayBuffer("Hello world"))));
+  it('decode "Hello world" after header when start < length', () => ok(testArrayBuffers(decode("data:image/bmp;base64,SGVsbG8gd29ybGQ=", 22), stringArrayBuffer("Hello world"))));
   it('decode all binary characters', () => ok(testArrayBuffers(decode("AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEyMzQ1Njc4OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWprbG1ub3BxcnN0dXZ3eHl6e3x9fn+AgYKDhIWGh4iJiouMjY6PkJGSk5SVlpeYmZqbnJ2en6ChoqOkpaanqKmqq6ytrq+wsbKztLW2t7i5uru8vb6/wMHCw8TFxsfIycrLzM3Oz9DR0tPU1dbX2Nna29zd3t/g4eLj5OXm5+jp6uvs7e7v8PHy8/T19vf4+fr7/P3+/w=="), rangeArrayBuffer())));
 });