diff --git a/lib/smpp/base.rb b/lib/smpp/base.rb
index ea91a71..651754a 100644
--- a/lib/smpp/base.rb
+++ b/lib/smpp/base.rb
@@ -162,7 +162,7 @@ def process_pdu(pdu)
         begin
           logger.debug "ESM CLASS #{pdu.esm_class}"
           case pdu.esm_class
-          when Pdu::Base::ESM_CLASS_DEFAULT, Pdu::Base::ESM_CLASS_DEFAULT_UDHI
+          when Pdu::Base::ESM_CLASS_DEFAULT, Pdu::Base::ESM_CLASS_DEFAULT_UDHI, Pdu::Base::ESM_CLASS_CUSTOM_UDHI
             # MO message
             run_callback(:mo_received, self, pdu)
           when Pdu::Base::ESM_CLASS_DELVR_REP, Pdu::Base::ESM_CLASS_DELVR_ACK, Pdu::Base::ESM_CLASS_USER_ACK, Pdu::Base::ESM_CLASS_INTER_ACK
diff --git a/lib/smpp/pdu/base.rb b/lib/smpp/pdu/base.rb
index 96fffcc..a7031fe 100644
--- a/lib/smpp/pdu/base.rb
+++ b/lib/smpp/pdu/base.rb
@@ -74,6 +74,7 @@ class Base
     ESM_CLASS_USER_ACK     = 16
     ESM_CLASS_INTER_ACK    = 32
     ESM_CLASS_DEFAULT_UDHI = 64
+    ESM_CLASS_CUSTOM_UDHI  = 67
 
     OPTIONAL_RECEIPTED_MESSAGE_ID = 0x001E
     OPTIONAL_MESSAGE_STATE        = 0x0427