diff --git a/app/assets/javascripts/app/lib/mixins/view_helpers.coffee b/app/assets/javascripts/app/lib/mixins/view_helpers.coffee
index 2d41d48e7..64686fd3c 100644
--- a/app/assets/javascripts/app/lib/mixins/view_helpers.coffee
+++ b/app/assets/javascripts/app/lib/mixins/view_helpers.coffee
@@ -155,6 +155,10 @@ App.ViewHelpers =
       return marked(string)
     App.i18n.translateContent(string)
 
+  ContentOrMimeType: (attachment) ->
+    types = ['Content-Type', 'content_type', 'Mime-Type', 'mime_type']
+    _.values(_.pick(attachment?.preferences, types))[0]
+
   ContentTypeIcon: (contentType) ->
     contentType = App.Utils.contentTypeCleanup(contentType)
     icons =
diff --git a/app/assets/javascripts/app/views/generic/attachments.jst.eco b/app/assets/javascripts/app/views/generic/attachments.jst.eco
index b1cc3907a..9f00bb4a7 100644
--- a/app/assets/javascripts/app/views/generic/attachments.jst.eco
+++ b/app/assets/javascripts/app/views/generic/attachments.jst.eco
@@ -9,7 +9,7 @@
           <div class="attachment-size"><%- @humanFileSize(attachment.size) %></div>
         </div>
       <% else: %>
-        <% content_type = attachment.preferences['Content-Type'] || attachment.preferences['content_type'] %>
+        <% content_type = @ContentOrMimeType(attachment) %>
         <a class="attachment attachment--preview" href="<%= attachment.url %>" data-type="attachment"<% if @canDownload(content_type): %> download<% else: %>target="_blank"<% end %>>
           <div class="attachment-icon">
           <% if attachment.preferences && content_type && @ContentTypeIcon(content_type): %>
@@ -28,4 +28,4 @@
       <% end %>
     <% end %>
   </div>
-<% end %>
\ No newline at end of file
+<% end %>
diff --git a/app/assets/javascripts/app/views/ticket_zoom/sidebar_article_attachment.jst.eco b/app/assets/javascripts/app/views/ticket_zoom/sidebar_article_attachment.jst.eco
index 7a0ba5748..b8bf35a33 100644
--- a/app/assets/javascripts/app/views/ticket_zoom/sidebar_article_attachment.jst.eco
+++ b/app/assets/javascripts/app/views/ticket_zoom/sidebar_article_attachment.jst.eco
@@ -1,13 +1,14 @@
 <div class="attachments-block js-attachments">
   <div class="attachments-block-headline"><%- @humanTime(@article.created_at) %></div>
   <% for attachment in @article.attachments: %>
-    <a class="attachment attachment--preview" title="<%- attachment.preferences['Content-Type'] %>" target="_blank" href="<%= App.Config.get('api_path') %>/ticket_attachment/<%= @article.ticket_id %>/<%= @article.id %>/<%= attachment.id %>?disposition=attachment" data-type="attachment"<% if @canDownload(attachment.preferences['Content-Type']): %> download<% end %>>
+    <% content_type = @ContentOrMimeType(attachment) %>
+    <a class="attachment attachment--preview" title="<%- content_type %>" target="_blank" href="<%= App.Config.get('api_path') %>/ticket_attachment/<%= @article.ticket_id %>/<%= @article.id %>/<%= attachment.id %>?disposition=attachment" data-type="attachment"<% if @canDownload(content_type): %> download<% end %>>
       <div class="attachment-icon">
-      <% if attachment.preferences && attachment.preferences['Content-Type'] && @ContentTypeIcon(attachment.preferences['Content-Type']): %>
-        <% if @canPreview(attachment.preferences['Content-Type']): %>
+      <% if content_type && @ContentTypeIcon(content_type): %>
+        <% if @canPreview(content_type): %>
           <img src="<%= App.Config.get('api_path') %>/ticket_attachment/<%= @article.ticket_id %>/<%= @article.id %>/<%= attachment.id %>?view=preview">
         <% else: %>
-          <%- @Icon( @ContentTypeIcon(attachment.preferences['Content-Type']) ) %>
+          <%- @Icon( @ContentTypeIcon(content_type) ) %>
         <% end %>
       <% else: %>
         <%- @Icon('file-unknown') %>
@@ -17,4 +18,4 @@
       <div class="attachment-size"><%- @humanFileSize(attachment.size) %></div>
     </a>
   <% end %>
-</div>
\ No newline at end of file
+</div>