diff --git a/app/helpers/favicon_helper.rb b/app/helpers/favicon_helper.rb
new file mode 100644
index 0000000000000000000000000000000000000000..3a5342a8d9d4cb388c889c11f3501f13dba36cac
--- /dev/null
+++ b/app/helpers/favicon_helper.rb
@@ -0,0 +1,7 @@
+module FaviconHelper
+  def favicon_extension_whitelist
+    FaviconUploader::EXTENSION_WHITELIST
+      .map { |extension| "'.#{extension}'"}
+      .to_sentence
+  end
+end
diff --git a/app/uploaders/favicon_uploader.rb b/app/uploaders/favicon_uploader.rb
index aa4c78da7a6b580bef246132a593cd26e1e963fc..09afc63a5aad8cfa41a01820fa1bc901305adc9b 100644
--- a/app/uploaders/favicon_uploader.rb
+++ b/app/uploaders/favicon_uploader.rb
@@ -1,4 +1,6 @@
 class FaviconUploader < AttachmentUploader
+  EXTENSION_WHITELIST = %w[png ico].freeze
+
   include CarrierWave::MiniMagick
 
   version :favicon_main do
@@ -11,7 +13,7 @@ class FaviconUploader < AttachmentUploader
   end
 
   def extension_whitelist
-    %w[png ico]
+    EXTENSION_WHITELIST
   end
 
   private
diff --git a/app/views/admin/appearances/_form.html.haml b/app/views/admin/appearances/_form.html.haml
index b44c006a459f347fcbc0e4ba03dc6b64d4b65f28..2e48364b94a7692afc1496524f6788cb92bcd618 100644
--- a/app/views/admin/appearances/_form.html.haml
+++ b/app/views/admin/appearances/_form.html.haml
@@ -72,7 +72,9 @@
       = f.hidden_field :favicon_cache
       = f.file_field :favicon, class: ''
       .hint
-        Maximum file size is 1MB. The resulting favicons will be cropped to be square and scaled down to a size of 32x32 px.
+        Maximum file size is 1MB. Allowed image formats are #{favicon_extension_whitelist}.
+        %br
+        The resulting favicons will be cropped to be square and scaled down to a size of 32x32 px.
 
   .form-actions
     = f.submit 'Save', class: 'btn btn-save append-right-10'