diff --git a/app/controllers/api/comments_controller.rb b/app/controllers/api/comments_controller.rb
index ab6ec89..07412df 100644
--- a/app/controllers/api/comments_controller.rb
+++ b/app/controllers/api/comments_controller.rb
@@ -38,7 +38,7 @@ class Api::CommentsController < ApplicationController
   end
 
   def notify_via_email(user, comment)
-    if user.email.present? && user != comment.user
+    if user && user.email.present? && user != comment.user
       UserMailer.new_comment_email(user, comment).deliver
     end
   end
diff --git a/spec/controllers/api/comments_controller_spec.rb b/spec/controllers/api/comments_controller_spec.rb
index c2fecd4..b9ff9f8 100644
--- a/spec/controllers/api/comments_controller_spec.rb
+++ b/spec/controllers/api/comments_controller_spec.rb
@@ -141,5 +141,14 @@ describe Api::CommentsController do
         @controller.send(:notify_via_email, user, comment)
       end
     end
+
+    context 'when asciicast author is unknown (nil)' do
+      let(:user) { nil }
+
+      it "doesn't send email" do
+        UserMailer.should_not_receive(:new_comment_email)
+        @controller.send(:notify_via_email, user, comment)
+      end
+    end
   end
 end