diff --git a/Gemfile b/Gemfile
index b523846fa..c5ad68913 100644
--- a/Gemfile
+++ b/Gemfile
@@ -78,7 +78,7 @@ gem 'sneaky-save', git: 'https://github.com/einzige/sneaky-save'
 gem 'turbolinks', '~> 5.1.1'
 gem 'underscore-rails'
 gem 'wicked_pdf', '~> 1.1.0'
-gem 'wkhtmltopdf-heroku'
+gem 'wkhtmltopdf-heroku', '2.12.4'
 
 gem 'aws-sdk-rails'
 gem 'aws-sdk-s3'
diff --git a/Gemfile.lock b/Gemfile.lock
index c2297e6d7..81e522c6c 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -558,7 +558,7 @@ GEM
     websocket-extensions (0.1.4)
     whacamole (1.2.0)
     wicked_pdf (1.1.0)
-    wkhtmltopdf-heroku (2.12.5.0)
+    wkhtmltopdf-heroku (2.12.4.0)
     xpath (3.2.0)
       nokogiri (~> 1.8)
     yomu (0.2.4)
@@ -671,7 +671,7 @@ DEPENDENCIES
   webpacker (~> 3.5)
   whacamole
   wicked_pdf (~> 1.1.0)
-  wkhtmltopdf-heroku
+  wkhtmltopdf-heroku (= 2.12.4)
   yomu
 
 RUBY VERSION
diff --git a/app/models/asset.rb b/app/models/asset.rb
index 7c1faca30..5bf4a7675 100644
--- a/app/models/asset.rb
+++ b/app/models/asset.rb
@@ -257,7 +257,7 @@ class Asset < ApplicationRecord
   end
 
   def image?
-    content_type == %r{^image/#{Regexp.union(Constants::WHITELISTED_IMAGE_TYPES)}}
+    content_type =~ %r{^image/#{Regexp.union(Constants::WHITELISTED_IMAGE_TYPES)}}
   end
 
   def text?
diff --git a/app/models/concerns/tiny_mce_images.rb b/app/models/concerns/tiny_mce_images.rb
index b5cc990f2..02f5e9b53 100644
--- a/app/models/concerns/tiny_mce_images.rb
+++ b/app/models/concerns/tiny_mce_images.rb
@@ -18,7 +18,7 @@ module TinyMceImages
       description = TinyMceAsset.update_old_tinymce(description, self)
 
       tiny_mce_assets.each do |tm_asset|
-        tm_asset_key = tm_asset.image.preview.key
+        tm_asset_key = tm_asset.preview.key
         encoded_tm_asset = Base64.strict_encode64(tm_asset.image.service.download(tm_asset_key))
         new_tm_asset_src = "data:image/jpg;base64,#{encoded_tm_asset}"
         html_description = Nokogiri::HTML(description)