diff --git a/test/functional/gantts_controller_test.rb b/test/functional/gantts_controller_test.rb
index ec73dd5ca..e1f9be8fa 100644
--- a/test/functional/gantts_controller_test.rb
+++ b/test/functional/gantts_controller_test.rb
@@ -155,7 +155,7 @@ class GanttsControllerTest < Redmine::ControllerTest
     assert @response.body.starts_with?('%PDF')
   end
 
-  if Object.const_defined?(:MiniMagick)
+  if Object.const_defined?(:MiniMagick) && convert_installed?
     def test_gantt_should_export_to_png
       get :show, :params => {
           :project_id => 1,
diff --git a/test/functional/issues_controller_test.rb b/test/functional/issues_controller_test.rb
index cb8a6703b..ca02c6dcd 100644
--- a/test/functional/issues_controller_test.rb
+++ b/test/functional/issues_controller_test.rb
@@ -2525,6 +2525,7 @@ class IssuesControllerTest < Redmine::ControllerTest
   end
 
   def test_show_with_thumbnails_enabled_should_display_thumbnails
+    skip unless convert_installed?
     @request.session[:user_id] = 2
     with_settings :thumbnails_enabled => '1' do
       get(:show, :params => {:id => 14})
diff --git a/test/helpers/journals_helper_test.rb b/test/helpers/journals_helper_test.rb
index 3c61388a1..a3475c6ab 100644
--- a/test/helpers/journals_helper_test.rb
+++ b/test/helpers/journals_helper_test.rb
@@ -32,6 +32,7 @@ class JournalsHelperTest < Redmine::HelperTest
            :versions
 
   def test_journal_thumbnail_attachments_should_return_thumbnailable_attachments
+    skip unless convert_installed?
     set_tmp_attachments_directory
     issue = Issue.generate!
 
diff --git a/test/integration/api_test/attachments_test.rb b/test/integration/api_test/attachments_test.rb
index 85dd895c0..4d83195c4 100644
--- a/test/integration/api_test/attachments_test.rb
+++ b/test/integration/api_test/attachments_test.rb
@@ -50,6 +50,7 @@ class Redmine::ApiTest::AttachmentsTest < Redmine::ApiTest::Base
   end
 
   test "GET /attachments/:id.xml for image should include thumbnail_url" do
+    skip unless convert_installed?
     get '/attachments/16.xml', :headers => credentials('jsmith')
     assert_response :success
     assert_equal 'application/xml', @response.media_type
diff --git a/test/unit/attachment_test.rb b/test/unit/attachment_test.rb
index 5c32d1e75..209775514 100644
--- a/test/unit/attachment_test.rb
+++ b/test/unit/attachment_test.rb
@@ -444,6 +444,7 @@ class AttachmentTest < ActiveSupport::TestCase
   end
 
   def test_thumbnailable_should_be_true_for_images
+    skip unless convert_installed?
     assert_equal true, Attachment.new(:filename => 'test.jpg').thumbnailable?
   end