diff --git a/README.md b/README.md
index 8be6ffe..e6c75e9 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,8 @@ In production mode, `strong-error-handler` omits details from error responses to
 - For 5xx errors, the output contains only the status code and the status name from the HTTP specification.
 - For 4xx errors, the output contains the full error message (`error.message`) and the contents of the `details`
   property (`error.details`) that `ValidationError` typically uses to provide machine-readable details
-  about validation problems.
+  about validation problems. It also includes `error.code` to allow a machine-readable error code to be passed
+  through which could be used, for example, for translation.
 
 In debug mode, `strong-error-handler` returns full error stack traces and internal details of any error objects to the client in the HTTP responses.
 
@@ -204,13 +205,13 @@ For more information, see
 
 ## Example
 
-Error generated when `debug: false` :
+5xx error generated when `debug: false` :
 
 ```
 { error: { statusCode: 500, message: 'Internal Server Error' } }
 ```
 
-Error generated when `debug: true` :
+The same error generated when `debug: true` :
 
 ```
 { error:
@@ -230,3 +231,14 @@ Error generated when `debug: true` :
   at tryOnImmediate (timers.js:543:15)    
   at processImmediate [as _immediateCallback] (timers.js:523:5)' }}
 ```
+
+4xx error generated when `debug: false` :
+
+```
+{ error:
+  { statusCode: 422,
+  name: 'Unprocessable Entity',
+  message: 'Missing required fields',
+  code: 'MISSING_REQUIRED_FIELDS' }}
+```
+
diff --git a/lib/data-builder.js b/lib/data-builder.js
index 40fbfe9..5505d31 100644
--- a/lib/data-builder.js
+++ b/lib/data-builder.js
@@ -77,6 +77,7 @@ function fillDebugData(data, err) {
 function fillBadRequestError(data, err) {
   data.name = err.name;
   data.message = err.message;
+  data.code = err.code;
   data.details = err.details;
 }
 
diff --git a/test/handler.test.js b/test/handler.test.js
index 86b6a81..1e533ed 100644
--- a/test/handler.test.js
+++ b/test/handler.test.js
@@ -193,6 +193,7 @@ describe('strong-error-handler', function() {
     it('contains all error properties when debug=true', function(done) {
       var error = new ErrorWithProps({
         message: 'a test error message',
+        code: 'MACHINE_READABLE_CODE',
         details: 'some details',
         extra: 'sensitive data',
       });
@@ -205,6 +206,7 @@ describe('strong-error-handler', function() {
           statusCode: 500,
           message: 'a test error message',
           name: 'ErrorWithProps',
+          code: 'MACHINE_READABLE_CODE',
           details: 'some details',
           extra: 'sensitive data',
           stack: error.stack,
@@ -215,6 +217,52 @@ describe('strong-error-handler', function() {
       });
     });
 
+    it('includes code property for 4xx status codes when debug=false',
+    function(done) {
+      var error = new ErrorWithProps({
+        statusCode: 400,
+        message: 'error with code',
+        name: 'ErrorWithCode',
+        code: 'MACHINE_READABLE_CODE',
+      });
+      givenErrorHandlerForError(error, {debug: false});
+
+      requestJson().end(function(err, res) {
+        if (err) return done(err);
+
+        var expectedData = {
+          statusCode: 400,
+          message: 'error with code',
+          name: 'ErrorWithCode',
+          code: 'MACHINE_READABLE_CODE',
+        };
+        expect(res.body).to.have.property('error');
+        expect(res.body.error).to.eql(expectedData);
+        done();
+      });
+    });
+
+    it('excludes code property for 5xx status codes when debug=false',
+    function(done) {
+      var error = new ErrorWithProps({
+        statusCode: 500,
+        code: 'MACHINE_READABLE_CODE',
+      });
+      givenErrorHandlerForError(error, {debug: false});
+
+      requestJson().end(function(err, res) {
+        if (err) return done(err);
+
+        var expectedData = {
+          statusCode: 500,
+          message: 'Internal Server Error',
+        };
+        expect(res.body).to.have.property('error');
+        expect(res.body.error).to.eql(expectedData);
+        done();
+      });
+    });
+
     it('contains non-enumerable Error properties when debug=true',
       function(done) {
         var error = new Error('a test error message');