diff --git a/app/models/mail_handler.rb b/app/models/mail_handler.rb
index be737931c..b502a86d7 100644
--- a/app/models/mail_handler.rb
+++ b/app/models/mail_handler.rb
@@ -145,7 +145,7 @@ class MailHandler < ActionMailer::Base
   private
 
   MESSAGE_ID_RE = %r{^<?redmine\.([a-z0-9_]+)\-(\d+)\.\d+(\.[a-f0-9]+)?@}
-  ISSUE_REPLY_SUBJECT_RE = %r{\[[^\]]*#(\d+)\]}
+  ISSUE_REPLY_SUBJECT_RE = %r{\[(?:[^\]]*\s+)?#(\d+)\]}
   MESSAGE_REPLY_SUBJECT_RE = %r{\[[^\]]*msg(\d+)\]}
 
   def dispatch
diff --git a/test/unit/mail_handler_test.rb b/test/unit/mail_handler_test.rb
index 6d250a4e2..d774eeedd 100644
--- a/test/unit/mail_handler_test.rb
+++ b/test/unit/mail_handler_test.rb
@@ -663,6 +663,30 @@ class MailHandlerTest < ActiveSupport::TestCase
     assert_equal 'Feature request', journal.issue.tracker.name
   end
 
+  def test_update_issue_should_accept_issue_id_after_space_inside_brackets
+    journal = submit_email('ticket_reply_with_status.eml') do |email|
+      assert email.sub!(/^Subject:.*$/, "Subject: Re: [Feature request #2] Add ingredients categories")
+    end
+    assert journal.is_a?(Journal)
+    assert_equal Issue.find(2), journal.journalized
+  end
+
+  def test_update_issue_should_accept_issue_id_inside_brackets
+    journal = submit_email('ticket_reply_with_status.eml') do |email|
+      assert email.sub!(/^Subject:.*$/, "Subject: Re: [#2] Add ingredients categories")
+    end
+    assert journal.is_a?(Journal)
+    assert_equal Issue.find(2), journal.journalized
+  end
+
+  def test_update_issue_should_ignore_bogus_issue_ids_in_subject
+    journal = submit_email('ticket_reply_with_status.eml') do |email|
+      assert email.sub!(/^Subject:.*$/, "Subject: Re: [12345#1][bogus#1][Feature request #2] Add ingredients categories")
+    end
+    assert journal.is_a?(Journal)
+    assert_equal Issue.find(2), journal.journalized
+  end
+
   def test_update_issue_with_attribute_changes
     # This email contains: 'Status: Resolved'
     journal = submit_email('ticket_reply_with_status.eml')