diff --git a/copy-to.js b/copy-to.js
index da10d03..6eefc36 100644
--- a/copy-to.js
+++ b/copy-to.js
@@ -4,6 +4,7 @@ module.exports = function(txt, options) {
 
 var Transform = require('stream').Transform
 var util = require('util')
+var code = require('./message-formats')
 
 var CopyStreamQuery = function(text, options) {
   Transform.call(this, options)
@@ -23,13 +24,6 @@ CopyStreamQuery.prototype.submit = function(connection) {
   connection.stream.pipe(this)
 }
 
-var code = {
-  E: 69, //Error
-  H: 72, //CopyOutResponse
-  d: 0x64, //CopyData
-  c: 0x63 //CopyDone
-}
-
 CopyStreamQuery.prototype._detach = function() {
   this.connection.stream.unpipe(this)
   // Unpipe can drop us out of flowing mode
@@ -44,13 +38,13 @@ CopyStreamQuery.prototype._transform = function(chunk, enc, cb) {
   }
   if(!this._copyOutResponse) {
     this._copyOutResponse = true
-    if(chunk[0] == code.E) {
+    if(chunk[0] == code.ErrorResponse) {
       this._detach()
       this.push(null)
       return cb();
     }
-    if(chunk[0] != code.H) {
-      this.emit('error', new Error('Expected copy out response'))
+    if(chunk[0] != code.CopyOutResponse) {
+      this.emit('error', new Error('Expected CopyOutResponse code (H)'))
     }
     var length = chunk.readUInt32BE(1)
     offset = 1
@@ -59,14 +53,14 @@ CopyStreamQuery.prototype._transform = function(chunk, enc, cb) {
   while((chunk.length - offset) > 5) {
     var messageCode = chunk[offset]
     //complete or error
-    if(messageCode == code.c || messageCode == code.E) {
+    if(messageCode == code.CopyDone || messageCode == code.ErrorResponse) {
       this._detach()
       this.push(null)
       return cb();
     }
     //something bad happened
-    if(messageCode != code.d) {
-      return this.emit('error', new Error('expected "d" (copydata message)'))
+    if(messageCode != code.CopyData) {
+      return this.emit('error', new Error('Expected CopyData code (d)'))
     }
     var length = chunk.readUInt32BE(offset + 1) - 4 //subtract length of UInt32
     //can we read the next row?
diff --git a/index.js b/index.js
index 9873c1f..25e02c2 100644
--- a/index.js
+++ b/index.js
@@ -10,6 +10,7 @@ module.exports = {
 
 var Transform = require('stream').Transform
 var util = require('util')
+var code = require('./message-formats')
 
 var CopyStreamQuery = function(text, options) {
   Transform.call(this, options)
@@ -26,13 +27,8 @@ CopyStreamQuery.prototype.submit = function(connection) {
   connection.query(this.text)
 }
 
-var code = {
-  H: 72, //CopyOutResponse
-  d: 0x64, //CopyData
-  c: 0x63 //CopyDone
-}
 
-var copyDataBuffer = Buffer([code.d])
+var copyDataBuffer = Buffer([code.CopyData])
 CopyStreamQuery.prototype._transform = function(chunk, enc, cb) {
   this.push(copyDataBuffer)
   var lenBuffer = Buffer(4)
@@ -43,7 +39,7 @@ CopyStreamQuery.prototype._transform = function(chunk, enc, cb) {
 }
 
 CopyStreamQuery.prototype._flush = function(cb) {
-  var finBuffer = Buffer([code.c, 0, 0, 0, 4])
+  var finBuffer = Buffer([code.CopyDone, 0, 0, 0, 4])
   this.push(finBuffer)
   cb()
 }
diff --git a/message-formats.js b/message-formats.js
new file mode 100644
index 0000000..9827498
--- /dev/null
+++ b/message-formats.js
@@ -0,0 +1,17 @@
+/**
+ * The COPY feature uses the following protocol codes.
+ * The codes for the most recent protocol version are documented on
+ * https://www.postgresql.org/docs/current/static/protocol-message-formats.html
+ * 
+ * The protocol flow itself is described on
+ * https://www.postgresql.org/docs/current/static/protocol-flow.html
+ */
+module.exports = {
+  ErrorResponse:    0x45,
+  CopyInResponse:   0x47,
+  CopyOutResponse:  0x48,
+  CopyBothResponse: 0x57,
+  CopyData:         0x64,
+  CopyDone:         0x63,
+  CopyFail:         0x66
+}