diff --git a/index.js b/index.js
index 5c62ea3..5ba7b3c 100644
--- a/index.js
+++ b/index.js
@@ -16,7 +16,7 @@ module.exports = function createGenerator(pattern, options) {
   var context = options && typeof options.context === 'string'
     ? options.context
     : '';
-  var hashPrefix = options && typeof options.hashPrefix
+  var hashPrefix = options && typeof options.hashPrefix === 'string'
     ? options.hashPrefix
     : '';
 
diff --git a/test.js b/test.js
index e48f549..32d66db 100644
--- a/test.js
+++ b/test.js
@@ -6,11 +6,16 @@ describe('generic-names', function () {
 
   it('should use cwd if no context provided', function () {
     var generate = genericNames('[name]__[local]___[hash:base64:5]');
-    assert.equal(generate('foo', '/test/case/source.css'), 'source__foo___2bpA4');
+    assert.equal(generate('foo', '/test/case/source.css'), 'source__foo___2e670');
   });
 
   it('should generate another hash for the provided context', function () {
     var generate = genericNames('[name]__[local]___[hash:base64:5]', {context: '/test'});
-    assert.equal(generate('foo', '/test/case/source.css'), 'source__foo___CEQPZ');
+    assert.equal(generate('foo', '/test/case/source.css'), 'source__foo___19xFw');
+  });
+
+  it('should generate another hash for the provided hashPrefix', function () {
+    var generate = genericNames('[name]__[local]___[hash:base64:5]', {context: '/test', hashPrefix: '--'});
+    assert.equal(generate('foo', '/test/case/source.css'), 'source__foo___3T0Un');
   });
 });