diff --git a/Readme.md b/Readme.md
index 78291ab8f..c415bf1e3 100644
--- a/Readme.md
+++ b/Readme.md
@@ -850,9 +850,21 @@ connection.query({
   }
 });
 ```
+__WARNING: YOU MUST INVOKE the parser using one of these three field functions in your custom typeCast callback. They can only be called once.( see #539 for discussion)__
+
+```
+field.string()
+field.buffer()
+field.geometry()
+```
+are aliases for
+```
+parser.parseLengthCodedString()
+parser.parseLengthCodedBuffer()
+parser.parseGeometryValue()
+```
+__You can find which field function you need to use by looking at: [RowDataPacket.prototype._typeCast](https://github.com/felixge/node-mysql/blob/master/lib/protocol/packets/RowDataPacket.js#L41)__
 
-If you need a buffer there's also a `.buffer()` function and also a `.geometry()` one
-both used by the default type cast that you can use.
 
 ## Connection Flags