diff --git a/slugify.js b/slugify.js
index dd13ebf..a286258 100644
--- a/slugify.js
+++ b/slugify.js
@@ -36,6 +36,7 @@
         var appendChar = locale[ch];
         if (appendChar === undefined) appendChar = charMap[ch];
         if (appendChar === undefined) appendChar = ch;
+        if (appendChar === null) appendChar = '';
         if (appendChar === replacement) appendChar = ' ';
         return result + appendChar
           // remove not allowed characters
diff --git a/test/slugify.js b/test/slugify.js
index 356c4b7..0d26c97 100644
--- a/test/slugify.js
+++ b/test/slugify.js
@@ -285,4 +285,13 @@ describe('slugify', () => {
     delete require.cache[require.resolve('../')]
     slugify = require('../')
   })
+
+  it('should correctly handle null values in extend() as character removal', () => {
+    slugify.extend({ '%': null, '$': null })
+    t.equal(slugify('100%'), '100')
+    t.equal(slugify('a$b%c'), 'abc')
+
+    delete require.cache[require.resolve('../')]
+    slugify = require('../')
+  })
 })