diff --git a/lib/b64.js b/lib/b64.js
index 70f12c9..46001d2 100644
--- a/lib/b64.js
+++ b/lib/b64.js
@@ -12,12 +12,16 @@ var lookup = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
 	var NUMBER = '0'.charCodeAt(0)
 	var LOWER  = 'a'.charCodeAt(0)
 	var UPPER  = 'A'.charCodeAt(0)
+	var PLUS_URL_SAFE = '-'.charCodeAt(0)
+	var SLASH_URL_SAFE = '_'.charCodeAt(0)
 
 	function decode (elt) {
 		var code = elt.charCodeAt(0)
-		if (code === PLUS)
+		if (code === PLUS ||
+		    code === PLUS_URL_SAFE)
 			return 62 // '+'
-		if (code === SLASH)
+		if (code === SLASH ||
+		    code === SLASH_URL_SAFE)
 			return 63 // '/'
 		if (code < NUMBER)
 			return -1 //no match
diff --git a/test/url-safe.js b/test/url-safe.js
new file mode 100644
index 0000000..dc437e9
--- /dev/null
+++ b/test/url-safe.js
@@ -0,0 +1,18 @@
+var test = require('tape'),
+  b64 = require('../lib/b64');
+
+test('decode url-safe style base64 strings', function (t) {
+  var expected = [0xff, 0xff, 0xbe, 0xff, 0xef, 0xbf, 0xfb, 0xef, 0xff];
+
+  var actual = b64.toByteArray('//++/++/++//');
+  for (var i = 0; i < actual.length; i++) {
+    t.equal(actual[i], expected[i])
+  }
+
+  actual = b64.toByteArray('__--_--_--__');
+  for (var i = 0; i < actual.length; i++) {
+    t.equal(actual[i], expected[i])
+  }
+  
+  t.end();
+});