diff --git a/config/initializers/10-patches.rb b/config/initializers/10-patches.rb
index e0559903b..f81d2b18e 100644
--- a/config/initializers/10-patches.rb
+++ b/config/initializers/10-patches.rb
@@ -107,6 +107,18 @@ end
 
 require 'mail'
 
+module Mail
+  class SubjectField
+    def initialize(value = nil, charset = 'utf-8')
+      if mime_encode = /^(=\?\S+\?\S\?)/.match(value).to_a[1]
+        value.gsub!(/\?=\s+#{Regexp.escape(mime_encode)}/, '')
+      end
+      self.charset = charset
+      super(CAPITALIZED_FIELD, value, charset)
+    end
+  end
+end
+
 module DeliveryMethods
   class TmpFile
     def initialize(*args); end
diff --git a/test/fixtures/mail_handler/ticket_with_split_bytes_subject.eml b/test/fixtures/mail_handler/ticket_with_split_bytes_subject.eml
new file mode 100644
index 000000000..9a9bf1407
--- /dev/null
+++ b/test/fixtures/mail_handler/ticket_with_split_bytes_subject.eml
@@ -0,0 +1,9 @@
+Date: Mon, 13 May 2019 13:39:29 +0900
+Message-ID: <CALXUZfgwpW-hizEabSAjjkykQGV6-V6bwKu693Cr7cDH6DR7pQ@mail.gmail.com>
+Subject: =?utf-8?B?zrHOss6zzrTOtc62zrfOuM65zrrOu868zr3Ovs6/z4DPgc+Cz4PPhM+Fz4bP?=
+        =?utf-8?B?h8+Iz4k=?=
+From: <foo@example.com>
+To: <baz@example.com>
+Content-Type: text/plain
+
+Split bytes subject.
diff --git a/test/unit/mail_handler_test.rb b/test/unit/mail_handler_test.rb
index 61b60434f..aab9cdddf 100644
--- a/test/unit/mail_handler_test.rb
+++ b/test/unit/mail_handler_test.rb
@@ -1136,6 +1136,17 @@ class MailHandlerTest < ActiveSupport::TestCase
     assert_equal issue.subject, 'New ticket on a given project with a very long subject line which exceeds 255 chars and should not be ignored but chopped off. And if the subject line is still not long enough, we just add more text. And more text. Wow, this is really annoying. Especially, if you have nothing to say...'[0,255]
   end
 
+  def test_email_with_split_bytes_subject
+    issue = submit_email(
+              'ticket_with_split_bytes_subject.eml',
+              :issue => {:project => 'ecookbook'},
+              :no_permission_check => '1',
+              :unknown_user => 'accept'
+            )
+    assert issue.is_a?(Issue)
+    assert_equal 'αβγδεζηθικλμνξοπρςστυφχψω', issue.subject
+  end
+
   def test_first_keyword_should_be_matched
     issue = submit_email('ticket_with_duplicate_keyword.eml', :allow_override => 'priority')
     assert issue.is_a?(Issue)