diff --git a/slug.js b/slug.js
index fb95d99..ceebea7 100644
--- a/slug.js
+++ b/slug.js
@@ -10,14 +10,15 @@ function symbols(code) {
 }
 
 function slug(string, opts) {
-    opts = opts || {};
     string = string.toString();
     if ('string' === typeof opts)
         opts = {replacement:opts};
+    opts = opts || {};
     opts.mode = opts.mode || slug.defaults.mode;
     var defaults = slug.defaults.modes[opts.mode];
     ['replacement','multicharmap','charmap','remove'].forEach(function (key) {
-        opts[key] = opts[key] || defaults[key];
+        if ('replacement' !== key || 'string' !== typeof opts[key])
+            opts[key] =  opts[key] || defaults[key];
     });
     if ('undefined' === typeof opts.symbols)
         opts.symbols = defaults.symbols;
diff --git a/test/slug.test.coffee b/test/slug.test.coffee
index 3aa690b..fe2e717 100644
--- a/test/slug.test.coffee
+++ b/test/slug.test.coffee
@@ -8,6 +8,7 @@ describe 'slug', ->
     it 'should replace whitespaces with replacement', ->
         [slug 'foo bar baz'].should.eql ['foo-bar-baz']
         [slug 'foo bar baz', '_'].should.eql ['foo_bar_baz']
+        [slug 'foo bar baz', ''].should.eql ['foobarbaz']
 
     it 'should remove trailing space if any', ->
         [slug ' foo bar baz '].should.eql ['foo-bar-baz']