diff --git a/app/views/hooks/redmine_dmsf/_view_mailer_issue.html.erb b/app/views/hooks/redmine_dmsf/_view_mailer_issue.html.erb
index 79c12d74..a37b0eb6 100644
--- a/app/views/hooks/redmine_dmsf/_view_mailer_issue.html.erb
+++ b/app/views/hooks/redmine_dmsf/_view_mailer_issue.html.erb
@@ -23,7 +23,7 @@
   <fieldset class="attachments"><legend><%= l(:label_dmsf_file_plural) %></legend>
     <% issue.dmsf_files.each do |f| %>
       <%= link_to h(f.name), static_dmsf_file_url(f, filename: f.name) %>
-      (<%= number_to_human_size(f.last_revision.size) %>)<br>
+      (<%= number_to_human_size(f.last_revision.size) if f.last_revision %>)<br>
     <% end %>
   </fieldset>
 <% end %>
diff --git a/app/views/hooks/redmine_dmsf/_view_mailer_issue.text.erb b/app/views/hooks/redmine_dmsf/_view_mailer_issue.text.erb
index dd93622e..b3b5d8cc 100644
--- a/app/views/hooks/redmine_dmsf/_view_mailer_issue.text.erb
+++ b/app/views/hooks/redmine_dmsf/_view_mailer_issue.text.erb
@@ -21,6 +21,6 @@
 <% if issue.dmsf_files.any? %>
   ---<%= l(:label_dmsf_file_plural).ljust(37, '-') %>
   <% issue.dmsf_files.each do |f| %>
-    <%= f.name %> (<%= number_to_human_size(f.last_revision.size) %>)
+    <%= f.name %> (<%= number_to_human_size(f.last_revision.size) if f.last_revision %>)
   <% end %>
 <% end %>