diff --git a/lib/urlsafe-base64.js b/lib/urlsafe-base64.js
index 7f26afa..78d4430 100644
--- a/lib/urlsafe-base64.js
+++ b/lib/urlsafe-base64.js
@@ -29,6 +29,7 @@ exports.version = '1.0.0';
  */
 
 exports.encode = function encode(buffer) {
+  if (!Buffer.isBuffer(buffer)) throw new TypeError('The input should be a buffer.')
 
   return buffer.toString('base64')
     .replace(/\+/g, '-') // Convert '+' to '-'
@@ -74,4 +75,4 @@ exports.validate = function validate(base64) {
 
   return /^[A-Za-z0-9\-_]+$/.test(base64);
 
-};
\ No newline at end of file
+};