diff --git a/bacnet-stack/demo/object/ao.c b/bacnet-stack/demo/object/ao.c
index b967885e..00df4fc7 100644
--- a/bacnet-stack/demo/object/ao.c
+++ b/bacnet-stack/demo/object/ao.c
@@ -238,11 +238,11 @@ int Analog_Output_Encode_Property_APDU(uint8_t * apdu,
             if (array_index <= BACNET_MAX_PRIORITY) {
                 if (Analog_Output_Level[object_index][array_index] ==
                     AO_LEVEL_NULL)
-                    len = encode_tagged_null(&apdu[apdu_len]);
+                    apdu_len = encode_tagged_null(&apdu[0]);
                 else {
                     real_value =
                         Analog_Output_Level[object_index][array_index];
-                    len = encode_tagged_real(&apdu[apdu_len], real_value);
+                    apdu_len = encode_tagged_real(&apdu[0], real_value);
                 }
             } else {
                 *error_class = ERROR_CLASS_PROPERTY;
diff --git a/bacnet-stack/demo/object/av.c b/bacnet-stack/demo/object/av.c
index 5146503b..ef9213c5 100644
--- a/bacnet-stack/demo/object/av.c
+++ b/bacnet-stack/demo/object/av.c
@@ -235,11 +235,11 @@ int Analog_Value_Encode_Property_APDU(uint8_t * apdu,
             if (array_index <= BACNET_MAX_PRIORITY) {
                 if (Analog_Value_Level[object_index][array_index] ==
                     ANALOG_LEVEL_NULL)
-                    len = encode_tagged_null(&apdu[apdu_len]);
+                    apdu_len = encode_tagged_null(&apdu[0]);
                 else {
                     real_value =
                         Analog_Value_Level[object_index][array_index];
-                    len = encode_tagged_real(&apdu[apdu_len], real_value);
+                    apdu_len = encode_tagged_real(&apdu[0], real_value);
                 }
             } else {
                 *error_class = ERROR_CLASS_PROPERTY;
diff --git a/bacnet-stack/demo/object/mso.c b/bacnet-stack/demo/object/mso.c
index e052ddcc..1d7479b3 100644
--- a/bacnet-stack/demo/object/mso.c
+++ b/bacnet-stack/demo/object/mso.c
@@ -238,12 +238,12 @@ int Multistate_Output_Encode_Property_APDU(uint8_t * apdu,
             if (array_index <= BACNET_MAX_PRIORITY) {
                 if (Multistate_Output_Level[object_index][array_index] ==
                     MULTISTATE_NULL)
-                    len = encode_tagged_null(&apdu[apdu_len]);
+                    apdu_len = encode_tagged_null(&apdu[0]);
                 else {
                     present_value =
                         Multistate_Output_Level[object_index][array_index];
-                    len =
-                        encode_tagged_unsigned(&apdu[apdu_len],
+                    apdu_len =
+                        encode_tagged_unsigned(&apdu[0],
                         present_value);
                 }
             } else {