diff --git a/index.js b/index.js
index 14f217d..42ab520 100644
--- a/index.js
+++ b/index.js
@@ -8,6 +8,7 @@ module.exports = {
     AlreadyExistsError: require('./lib/error/alreadyExistsError').AlreadyExistsError,
     UnknownValidateError: require('./lib/error/unknownValidateError').UnknownValidateError,
     InvalidPointOfSaleError: require('./lib/error/invalidPointOfSaleError').InvalidPointOfSaleError,
+    InvalidPurchaseOrderNumberError: require('./lib/error/invalidPurchaseOrderNumberError').InvalidPurchaseOrderNumberError,
     InvalidDateError: require('./lib/error/invalidDateError').InvalidDateError,
     InvalidAmountError: require('./lib/error/invalidAmountError').InvalidAmountError,
     InvalidTaxRegistrationNumberError: require('./lib/error/invalidTaxRegistrationNumberError').InvalidTaxRegistrationNumberError
diff --git a/lib/error/invalidPurchaseOrderNumberError.js b/lib/error/invalidPurchaseOrderNumberError.js
new file mode 100644
index 0000000..17b83be
--- /dev/null
+++ b/lib/error/invalidPurchaseOrderNumberError.js
@@ -0,0 +1,13 @@
+var util = require('util');
+
+var InvalidPurchaseOrderNumberError = function InvalidPurchaseOrderNumberError(message, userMessage, field) {
+  Error.call(this);
+  this.name = 'InvalidPurchaseOrderNumberError';
+  this.message = message;
+  this.userMessage = userMessage;
+  this.field = field;
+};
+
+util.inherits(InvalidPurchaseOrderNumberError, Error);
+
+module.exports.InvalidPurchaseOrderNumberError = InvalidPurchaseOrderNumberError;
\ No newline at end of file
diff --git a/package.json b/package.json
index e7eda05..0064bbc 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "receipts-model",
-  "version": "0.5.5",
+  "version": "0.5.6",
   "description": "Receipts model.",
   "main": "./index.js",
   "dependencies": {
@@ -42,6 +42,6 @@
     "node": ">=0.10.0"
   },
   "readmeFilename": "README.md",
-  "_id": "receipts-model@0.5.5",
-  "_from": "receipts-model@^0.5.5"
+  "_id": "receipts-model@0.5.6",
+  "_from": "receipts-model@^0.5.6"
 }
diff --git a/test/indexTest.js b/test/indexTest.js
index 1e64452..6d183ec 100644
--- a/test/indexTest.js
+++ b/test/indexTest.js
@@ -39,6 +39,13 @@ describe('index test', function () {
     done();
   });
 
+  it('should export InvalidPurchaseOrderNumberError', function (done) {
+
+    var InvalidPurchaseOrderNumberError = index.error.InvalidPurchaseOrderNumberError;
+    should.exist(InvalidPurchaseOrderNumberError);
+    done();
+  });
+
   it('should export InvalidDateError', function (done) {
 
     var InvalidDateError = index.error.InvalidDateError;