diff --git a/app/models/topic.rb b/app/models/topic.rb
index d78533fcd8b..c47d457fe5d 100644
--- a/app/models/topic.rb
+++ b/app/models/topic.rb
@@ -52,7 +52,7 @@ class Topic < ActiveRecord::Base
 
   def thumbnail_info(enqueue_if_missing: false, extra_sizes: [])
     return nil unless original = image_upload
-    return nil unless original.filesize < SiteSetting.max_image_size_kb
+    return nil unless original.filesize < SiteSetting.max_image_size_kb.kilobytes
     return nil unless original.read_attribute(:width) && original.read_attribute(:height)
 
     infos = []
@@ -95,7 +95,7 @@ class Topic < ActiveRecord::Base
   def generate_thumbnails!(extra_sizes: [])
     return nil unless SiteSetting.create_thumbnails
     return nil unless original = image_upload
-    return nil unless original.filesize < SiteSetting.max_image_size_kb
+    return nil unless original.filesize < SiteSetting.max_image_size_kb.kilobytes
     return nil unless original.width && original.height
     extra_sizes = [] unless extra_sizes.kind_of?(Array)
 
@@ -113,7 +113,7 @@ class Topic < ActiveRecord::Base
     if thumbnail.nil? &&
         image_upload &&
         SiteSetting.create_thumbnails &&
-        image_upload.filesize < SiteSetting.max_image_size_kb &&
+        image_upload.filesize < SiteSetting.max_image_size_kb.kilobytes &&
         enqueue_if_missing &&
         Discourse.redis.set(thumbnail_job_redis_key([]), 1, nx: true, ex: 1.minute)
       Jobs.enqueue(:generate_topic_thumbnails, { topic_id: id })
diff --git a/spec/models/topic_thumbnail_spec.rb b/spec/models/topic_thumbnail_spec.rb
index 92481241c4a..ab7ff72467f 100644
--- a/spec/models/topic_thumbnail_spec.rb
+++ b/spec/models/topic_thumbnail_spec.rb
@@ -4,10 +4,10 @@ require 'rails_helper'
 describe "TopicThumbnail" do
   let(:upload1) { Fabricate(:image_upload, width: 5000, height: 5000) }
   let(:topic) { Fabricate(:topic, image_upload: upload1) }
-
-  let(:upload2) { Fabricate(:image_upload, width: 5000, height: 5000, filesize: 8000) }
+  let(:upload2) { Fabricate(:image_upload, width: 5000, height: 5000) }
   let(:topic2) { Fabricate(:topic, image_upload: upload2) }
 
+
   before do
     SiteSetting.create_thumbnails = true
     topic.generate_thumbnails!(extra_sizes: nil)
@@ -19,6 +19,7 @@ describe "TopicThumbnail" do
   end
 
   it "does not enque job if original image is too large" do
+    upload2.filesize = SiteSetting.max_image_size_kb.kilobytes + 1
     SiteSetting.create_thumbnails = true
     topic2.generate_thumbnails!(extra_sizes: nil)