diff --git a/app/controllers/assets_controller.rb b/app/controllers/assets_controller.rb
index 3b2155550..a81b6b03b 100644
--- a/app/controllers/assets_controller.rb
+++ b/app/controllers/assets_controller.rb
@@ -114,8 +114,9 @@ class AssetsController < ApplicationController
       fields: s3_post.fields
     })
 
-    if (asset.file_content_type =~
-      %r{/^image\/#{Constants::WHITELISTED_IMAGE_TYPES.join("|")}/}) == 0
+    condition = %r{^image/#{Regexp.union(Constants::WHITELISTED_IMAGE_TYPES)}}
+
+    if condition === asset.file_content_type
       asset.file.options[:styles].each do |style, option|
         s3_post = S3_BUCKET.presigned_post(
           key: asset.file.path(style)[1..-1],
diff --git a/app/models/asset.rb b/app/models/asset.rb
index 50b91b5e5..ec4bec03d 100644
--- a/app/models/asset.rb
+++ b/app/models/asset.rb
@@ -138,8 +138,8 @@ class Asset < ActiveRecord::Base
   end
 
   def is_image?
-    !(file.content_type =~
-      %r{/^image\/#{Constants::WHITELISTED_IMAGE_TYPES.join("|")}/}).nil?
+    %r{^image/#{Regexp.union(Constants::WHITELISTED_IMAGE_TYPES)}} ===
+      file.content_type
   end
 
   def text?