diff --git a/app/models/theme.rb b/app/models/theme.rb
index c3fe321..812926e 100644
--- a/app/models/theme.rb
+++ b/app/models/theme.rb
@@ -49,7 +49,10 @@ class Theme
 
         approved = config['public']
         unless approved
-          approved = config['owner_type'] == owner.class.base_class.name || config['owner_type'] == owner.class.name
+          begin
+            approved = owner.kind_of?(config['owner_type'].constantize)
+          rescue
+          end
           approved &&= config['owner_id'] == owner.id if config['owner_id'].present?
         end
 
@@ -58,7 +61,6 @@ class Theme
         new id, config
       end
     end
-
   end
 
   class DuplicatedIdentifier < Exception; end
diff --git a/test/unit/theme_test.rb b/test/unit/theme_test.rb
index f8f21d7..c170ef5 100644
--- a/test/unit/theme_test.rb
+++ b/test/unit/theme_test.rb
@@ -191,4 +191,22 @@ class ThemeTest < ActiveSupport::TestCase
     assert ! Theme.new('test').public
   end
 
+  should 'not crash with nil or invalid owner_type' do
+    profile = fast_create(Profile)
+    Theme.stubs(:system_themes_dir).returns(TMP_THEMES_DIR)
+
+    t1 = Theme.new('t1').save
+    t1.send(:write_config)
+    t2 = Theme.new('t2', {:owner_type => nil}).save
+    t2.send(:write_config)
+    t3 = Theme.new('t3', {:owner_type => 'InvalidClass'}).save
+    t3.send(:write_config)
+
+    assert_nothing_raised do
+      themes = Theme.approved_themes(profile)
+      assert_not_includes themes, t1
+      assert_not_includes themes, t2
+      assert_not_includes themes, t3
+    end
+  end
 end
--
libgit2 0.21.2