diff --git a/lib/pardot/authentication.rb b/lib/pardot/authentication.rb
index b56f1c4..84821b8 100644
--- a/lib/pardot/authentication.rb
+++ b/lib/pardot/authentication.rb
@@ -3,7 +3,7 @@ module Authentication
     
     def authenticate
       resp = post "login", nil, :email => @email, :password => @password, :user_key => @user_key
-      @api_key = resp["api_key"]
+      @api_key = resp && resp["api_key"]
     end
     
     def authenticated?