diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 6f65d4003d..db3378d9d9 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,7 @@
 *Edge*
 
+* Made AbstractRequest.if_modified_sense return nil if the header could not be parsed [Jamis Buck]
+
 * Added back ActionController::Base.allow_concurrency flag [Josh Peek]
 
 * AbstractRequest.relative_url_root is no longer automatically configured by a HTTP header. It can now be set in your configuration environment with config.action_controller.relative_url_root [Josh Peek]
diff --git a/actionpack/lib/action_controller/request.rb b/actionpack/lib/action_controller/request.rb
index 90bced14e6..364e6201cc 100644
--- a/actionpack/lib/action_controller/request.rb
+++ b/actionpack/lib/action_controller/request.rb
@@ -100,7 +100,7 @@ module ActionController
 
     def if_modified_since
       if since = env['HTTP_IF_MODIFIED_SINCE']
-        Time.rfc2822(since)
+        Time.rfc2822(since) rescue nil
       end
     end
     memoize :if_modified_since