diff --git a/bacnet-stack/src/rp.c b/bacnet-stack/src/rp.c
index 477e244b..b3558a19 100644
--- a/bacnet-stack/src/rp.c
+++ b/bacnet-stack/src/rp.c
@@ -147,16 +147,23 @@ int rp_ack_encode_apdu_init(
 {
     int len = 0;        /* length of each encoding */
     int apdu_len = 0;   /* total length of the apdu, return value */
+    uint32_t obj_instance = rpdata->object_instance;
 
     if (apdu) {
         apdu[0] = PDU_TYPE_COMPLEX_ACK; /* complex ACK service */
         apdu[1] = invoke_id;    /* original invoke id from request */
         apdu[2] = SERVICE_CONFIRMED_READ_PROPERTY;      /* service choice */
         apdu_len = 3;
+        
+        /* Test for case of indefinite Device object instance */
+        if ( (rpdata->object_type == OBJECT_DEVICE) && 
+        	 (obj_instance == BACNET_MAX_INSTANCE) )
+        	obj_instance = Device_Object_Instance_Number();
+        
         /* service ack follows */
         len =
             encode_context_object_id(&apdu[apdu_len], 0, rpdata->object_type,
-            rpdata->object_instance);
+            		obj_instance);
         apdu_len += len;
         len =
             encode_context_enumerated(&apdu[apdu_len], 1,
@@ -198,25 +205,9 @@ int rp_ack_encode_apdu(
     int apdu_len = 0;   /* total length of the apdu, return value */
 
     if (apdu) {
-        apdu[0] = PDU_TYPE_COMPLEX_ACK; /* complex ACK service */
-        apdu[1] = invoke_id;    /* original invoke id from request */
-        apdu[2] = SERVICE_CONFIRMED_READ_PROPERTY;      /* service choice */
-        apdu_len = 3;
-        /* service ack follows */
-        apdu_len +=
-            encode_context_object_id(&apdu[apdu_len], 0, rpdata->object_type,
-            rpdata->object_instance);
-        apdu_len +=
-            encode_context_enumerated(&apdu[apdu_len], 1,
-            rpdata->object_property);
-        /* context 2 array index is optional */
-        if (rpdata->array_index != BACNET_ARRAY_ALL) {
-            apdu_len +=
-                encode_context_unsigned(&apdu[apdu_len], 2,
-                rpdata->array_index);
-        }
+    	/* Do the initial encoding */
+        apdu_len = rp_ack_encode_apdu_init(apdu, invoke_id, rpdata);
         /* propertyValue */
-        apdu_len += encode_opening_tag(&apdu[apdu_len], 3);
         for (len = 0; len < rpdata->application_data_len; len++) {
             apdu[apdu_len++] = rpdata->application_data[len];
         }
diff --git a/bacnet-stack/src/rpm.c b/bacnet-stack/src/rpm.c
index 6b6859bb..b60177dd 100644
--- a/bacnet-stack/src/rpm.c
+++ b/bacnet-stack/src/rpm.c
@@ -108,6 +108,14 @@ int rpm_encode_apdu_object_end(
     return apdu_len;
 }
 
+/** Encode an RPM request, to be sent.
+ * 
+ * @param apdu [in,out] Buffer to hold encoded bytes.
+ * @param max_apdu [in] Length of apdu buffer.
+ * @param invoke_id [in] The Invoke ID to use for this message.
+ * @param read_access_data [in] The RPM data to be requested.
+ * @return Length of encoded bytes, or 0 on failure.
+ */
 int rpm_encode_apdu(
     uint8_t * apdu,
     size_t max_apdu,
@@ -328,12 +336,18 @@ int rpm_ack_encode_apdu_object_begin(
     BACNET_RPM_DATA * rpmdata)
 {
     int apdu_len = 0;   /* total length of the apdu, return value */
+    uint32_t obj_instance = rpmdata->object_instance;
 
     if (apdu) {
+        /* Test for case of indefinite Device object instance */
+        if ( (rpmdata->object_type == OBJECT_DEVICE) && 
+        	 (obj_instance == BACNET_MAX_INSTANCE) )
+        	obj_instance = Device_Object_Instance_Number();
+
         /* Tag 0: objectIdentifier */
         apdu_len =
             encode_context_object_id(&apdu[0], 0, rpmdata->object_type,
-            rpmdata->object_instance);
+            		obj_instance);
         /* Tag 1: listOfResults */
         apdu_len += encode_opening_tag(&apdu[apdu_len], 1);
     }