diff --git a/lib/redmine_dmsf/webdav/project_resource.rb b/lib/redmine_dmsf/webdav/project_resource.rb
index c6b93eff..8a982f7a 100644
--- a/lib/redmine_dmsf/webdav/project_resource.rb
+++ b/lib/redmine_dmsf/webdav/project_resource.rb
@@ -122,7 +122,7 @@ module RedmineDmsf
           # 1. Invalid characters are replaced with a dot.
           # 2. Two or more dots in a row are replaced with a single dot.
           # (3. Windows WebClient does not like a dot at the end, but since the project id tag is appended this is not a problem.)
-          "#{p.name.gsub(DmsfFolder.INVALID_CHARACTERS, ".").gsub(/\.{2,}/, '.')} #{p.id}" unless p.nil?
+          "#{p.name.gsub(DmsfFolder::INVALID_CHARACTERS, ".").gsub(/\.{2,}/, '.')} #{p.id}" unless p.nil?
         else
           p.identifier unless p.nil?
         end