diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index dc333f67..0108b35d 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -56,7 +56,7 @@ module ApplicationHelper
   end
 
   def ios_web_app?
-    user_agent = request.env['HTTP_USER_AGENT']
+    user_agent = request.env['HTTP_USER_AGENT'] || 'Mozilla/5.0'
     # normal MobileSafari.app UA: Mozilla/5.0 (iPhone; CPU iPhone OS 8_1_1 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) Version/8.0 Mobile/12B435 Safari/600.1.4
     # webapp UA: Mozilla/5.0 (iPhone; CPU iPhone OS 8_1_1 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) Mobile/12B435
     return true if user_agent.match /^Mozilla\/\d+\.\d+ \(i(?:Phone|Pad|Pod); CPU(?:.*) like Mac OS X\)(?:.*) Mobile(?:\S*)$/