diff --git a/include/skipstone/message.h b/include/skipstone/message.h
index a827e6b..23716de 100644
--- a/include/skipstone/message.h
+++ b/include/skipstone/message.h
@@ -36,7 +36,7 @@ typedef struct _skipstone_message skipstone_message;
 typedef int (skipstone_message_handler)(skipstone_message_service *service,
         void *buf, uint16_t size, uint16_t id, void *context);
 
-skipstone_message *skipstone_message_new(uint16_t id);
+skipstone_message *skipstone_message_new();
 
 int skipstone_message_append_string(skipstone_message *message,
         char *string, uint8_t size);
diff --git a/src/message.c b/src/message.c
index bea7d93..2652578 100644
--- a/src/message.c
+++ b/src/message.c
@@ -19,8 +19,8 @@ struct part {
 };
 
 struct _skipstone_message {
-    uint16_t size, id;
     skipstone_queue *parts;
+    uint16_t size;
 };
 
 struct endpoint {
@@ -34,7 +34,7 @@ struct _skipstone_message_service {
     skipstone_queue *pending;
 };
 
-skipstone_message *skipstone_message_new(uint16_t id) {
+skipstone_message *skipstone_message_new() {
     skipstone_message *message;
 
     if ((message = malloc(sizeof(*message))) == NULL) {
@@ -46,7 +46,6 @@ skipstone_message *skipstone_message_new(uint16_t id) {
     }
 
     message->size = 0;
-    message->id   = id;
 
     return message;
 
@@ -86,17 +85,33 @@ error_malloc_part:
 
 int skipstone_message_append_string(skipstone_message *message,
         char *string, uint8_t size) {
-    return append_part(message, string, size, SKIPSTONE_MESSAGE_PART_STRING);
+    if (append_part(message, string, size, SKIPSTONE_MESSAGE_PART_STRING) < 0) {
+        return -1;
+    }
+
+    message->size += sizeof(size) + size;
+
+    return 0;
 }
 
 int skipstone_message_append_uint8(skipstone_message *message, uint8_t value) {
-    return append_part(message, &value, sizeof(value),
-        SKIPSTONE_MESSAGE_PART_UINT8);
+    if (append_part(message, &value, sizeof(value), SKIPSTONE_MESSAGE_PART_UINT8) < 0) {
+        return -1;
+    }
+
+    message->size += sizeof(value);
+
+    return 0;
 }
 
 int skipstone_message_append_uint16(skipstone_message *message, uint16_t value) {
-    return append_part(message, &value, sizeof(value),
-        SKIPSTONE_MESSAGE_PART_UINT16);
+    if (append_part(message, &value, sizeof(value), SKIPSTONE_MESSAGE_PART_UINT16) < 0) {
+        return -1;
+    }
+
+    message->size += sizeof(value);
+
+    return 0;
 }
 
 int skipstone_message_pack(skipstone_message *message,
diff --git a/src/message.c-e b/src/message.c-e
index bea7d93..2652578 100644
--- a/src/message.c-e
+++ b/src/message.c-e
@@ -19,8 +19,8 @@ struct part {
 };
 
 struct _skipstone_message {
-    uint16_t size, id;
     skipstone_queue *parts;
+    uint16_t size;
 };
 
 struct endpoint {
@@ -34,7 +34,7 @@ struct _skipstone_message_service {
     skipstone_queue *pending;
 };
 
-skipstone_message *skipstone_message_new(uint16_t id) {
+skipstone_message *skipstone_message_new() {
     skipstone_message *message;
 
     if ((message = malloc(sizeof(*message))) == NULL) {
@@ -46,7 +46,6 @@ skipstone_message *skipstone_message_new(uint16_t id) {
     }
 
     message->size = 0;
-    message->id   = id;
 
     return message;
 
@@ -86,17 +85,33 @@ error_malloc_part:
 
 int skipstone_message_append_string(skipstone_message *message,
         char *string, uint8_t size) {
-    return append_part(message, string, size, SKIPSTONE_MESSAGE_PART_STRING);
+    if (append_part(message, string, size, SKIPSTONE_MESSAGE_PART_STRING) < 0) {
+        return -1;
+    }
+
+    message->size += sizeof(size) + size;
+
+    return 0;
 }
 
 int skipstone_message_append_uint8(skipstone_message *message, uint8_t value) {
-    return append_part(message, &value, sizeof(value),
-        SKIPSTONE_MESSAGE_PART_UINT8);
+    if (append_part(message, &value, sizeof(value), SKIPSTONE_MESSAGE_PART_UINT8) < 0) {
+        return -1;
+    }
+
+    message->size += sizeof(value);
+
+    return 0;
 }
 
 int skipstone_message_append_uint16(skipstone_message *message, uint16_t value) {
-    return append_part(message, &value, sizeof(value),
-        SKIPSTONE_MESSAGE_PART_UINT16);
+    if (append_part(message, &value, sizeof(value), SKIPSTONE_MESSAGE_PART_UINT16) < 0) {
+        return -1;
+    }
+
+    message->size += sizeof(value);
+
+    return 0;
 }
 
 int skipstone_message_pack(skipstone_message *message,