diff --git a/config/locales/en.yml b/config/locales/en.yml
index 43b09a0729..b11a057e2e 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -647,7 +647,9 @@ en:
         attachment:
           attributes:
             content_type:
-              not_whitelisted: "is set to '%{value}', which is not whitelisted for uploading."
+              blank: "The content type of the file cannot be blank."
+              not_whitelisted: "The file was rejected by an automatic filter. '%{value}' is not whitelisted for upload."
+              format: "%{message}"
         capability:
           context:
             global: 'Global'
diff --git a/spec/requests/api/v3/attachments/attachment_resource_shared_examples.rb b/spec/requests/api/v3/attachments/attachment_resource_shared_examples.rb
index 00946f9548..3233e69d49 100644
--- a/spec/requests/api/v3/attachments/attachment_resource_shared_examples.rb
+++ b/spec/requests/api/v3/attachments/attachment_resource_shared_examples.rb
@@ -299,7 +299,7 @@ shared_examples 'an APIv3 attachment resource', type: :request, content_type: :j
       let(:request_parts) { { metadata: metadata.to_json, wrongFileSection: file } }
 
       it_behaves_like 'constraint violation' do
-        let(:message) { "Content type #{I18n.t('activerecord.errors.messages.blank')}" }
+        let(:message) { "The content type of the file cannot be blank" }
       end
     end
 
@@ -586,7 +586,7 @@ shared_examples 'an APIv3 attachment resource', type: :request, content_type: :j
         let(:request_parts) { { metadata: metadata.to_json, wrongFileSection: file } }
 
         it_behaves_like 'constraint violation' do
-          let(:message) { "Content type #{I18n.t('activerecord.errors.messages.blank')}" }
+          let(:message) { "The content type of the file cannot be blank." }
         end
       end