diff --git a/src/smpp34.h b/src/smpp34.h
index 9d51a4a..b66d47f 100644
--- a/src/smpp34.h
+++ b/src/smpp34.h
@@ -212,4 +212,8 @@
 #define SMPP34_UDHI_IND			0x40
 #define SMPP34_REPLY_PATH		0x80
 
+/* Sect. 5.2.17 registered_delivery. */
+#define SMPP34_DELIVERY_RECEIPT_OFF	0x00
+#define SMPP34_DELIVERY_RECEIPT_ON	0x01
+
 #endif