diff --git a/app/models/dmsf_file_revision.rb b/app/models/dmsf_file_revision.rb
index f0963513..1fbffb18 100644
--- a/app/models/dmsf_file_revision.rb
+++ b/app/models/dmsf_file_revision.rb
@@ -257,13 +257,14 @@ class DmsfFileRevision < ActiveRecord::Base
     else
       filename = self.name
     end
-    format.sub!('%t', self.title)
-    format.sub!('%f', filename)
-    format.sub!('%d', self.updated_at.strftime('%Y%m%d%H%M%S'))
-    format.sub!('%v', self.version)
-    format.sub!('%i', self.dmsf_file.id.to_s)
-    format.sub!('%r', self.id.to_s)
-    format + ext
+    format2 = format.dup
+    format2.sub!('%t', self.title)
+    format2.sub!('%f', filename)
+    format2.sub!('%d', self.updated_at.strftime('%Y%m%d%H%M%S'))
+    format2.sub!('%v', self.version)
+    format2.sub!('%i', self.dmsf_file.id.to_s)
+    format2.sub!('%r', self.id.to_s)
+    format2 + ext
   end
 
   def self.create_digest(path)