diff --git a/src/createClient.js b/src/createClient.js
index 2a4f4b4..f9f7d5d 100644
--- a/src/createClient.js
+++ b/src/createClient.js
@@ -92,7 +92,7 @@ function createClient(options) {
   }
 
   function onKeepAlive(packet) {
-    client.write(0x00, {
+    client.write('keep_alive', {
       keepAliveId: packet.keepAliveId
     });
   }
diff --git a/src/transforms/serializer.js b/src/transforms/serializer.js
index 9747739..62fdfab 100644
--- a/src/transforms/serializer.js
+++ b/src/transforms/serializer.js
@@ -78,7 +78,9 @@ function createPacketBuffer(packetId, state, params, isServer) {
       length += proto.sizeOf(params[fieldInfo.name], fieldInfo.type, params);
     }, (e) => {
       addErrorField(e, fieldInfo.name);
-      e.message = "sizeOf error for " + packetName + "." + e.field + " : " + e.message;
+      e.message = "sizeOf error for "+[state,direction,packetName,e.field].join(".")+"\n"+
+        " in packet 0x" + packetId.toString(16)+" "+JSON.stringify(params)+"\n"
+        + e.message;
       throw e;
     });
   });