diff --git a/lib/common/util.js b/lib/common/util.js
index f558dcb93c3..9a8e89c1729 100644
--- a/lib/common/util.js
+++ b/lib/common/util.js
@@ -14,17 +14,16 @@
  * limitations under the License.
  */
 
-/*jshint strict:false, noarg:false */
-
-/**
- * @private
+/*!
  * @module common/util
  */
 
+'use strict';
+
+var createErrorClass = require('create-error-class');
 var extend = require('extend');
 var googleAuth = require('google-auto-auth');
 var is = require('is');
-var nodeutil = require('util');
 var request = require('request').defaults({
   pool: {
     maxSockets: Infinity
@@ -109,24 +108,25 @@ function noop() {}
 util.noop = noop;
 
 /**
- * Extend the native Error object.
- *
- * @constructor
+ * Custom error type for API errors.
  *
  * @param {object} errorBody - Error object.
  */
-function ApiError(errorBody) {
-  Error.call(this);
-  Error.captureStackTrace(this, arguments.callee);
+var ApiError = createErrorClass('ApiError', function(errorBody) {
   this.errors = errorBody.errors;
   this.code = errorBody.code;
   this.message = errorBody.message || 'Error during request.';
   this.response = errorBody.response;
-}
-
-nodeutil.inherits(ApiError, Error);
+});
 
-util.ApiError = ApiError;
+/**
+ * Wrap the ApiError constructor so context isn't lost.
+ *
+ * @param {object} errorBody - Error object.
+ */
+util.ApiError = function(errorBody) {
+  return new ApiError(errorBody);
+};
 
 /**
  * Uniformly process an API response.
diff --git a/lib/storage/file.js b/lib/storage/file.js
index b4b08a968a2..f8a748827b8 100644
--- a/lib/storage/file.js
+++ b/lib/storage/file.js
@@ -21,6 +21,7 @@
 'use strict';
 
 var concat = require('concat-stream');
+var createErrorClass = require('create-error-class');
 var crypto = require('crypto');
 var duplexify = require('duplexify');
 var format = require('string-format-obj');
@@ -46,6 +47,16 @@ var Acl = require('./acl.js');
  */
 var util = require('../common/util.js');
 
+/**
+ * Custom error type for errors related to getting signed errors and policies.
+ *
+ * @param {string} message - Custom error message.
+ * @return {Error}
+ */
+var SigningError = createErrorClass('SigningError', function(message) {
+  this.message = message;
+});
+
 /**
  * @const {string}
  * @private
@@ -1066,19 +1077,17 @@ File.prototype.getSignedPolicy = function(options, callback) {
 
   makeAuthenticatedRequest_.getCredentials(function(err, credentials) {
     if (err) {
-      var signingError = new Error('Signing failed. See `error` property.');
-      signingError.error = err;
-      callback(signingError);
+      callback(new SigningError(err.message));
       return;
     }
 
     if (!credentials.private_key) {
       var errorMessage = [
-        'Signing failed. Could not find a `private_key`.',
+        'Could not find a `private_key`.',
         'Please verify you are authorized with this property available.'
       ].join(' ');
 
-      callback(new Error(errorMessage));
+      callback(new SigningError(errorMessage));
       return;
     }
 
@@ -1197,19 +1206,17 @@ File.prototype.getSignedUrl = function(options, callback) {
 
   makeAuthenticatedRequest_.getCredentials(function(err, credentials) {
     if (err) {
-      var signingError = new Error('Signing failed. See `error` property.');
-      signingError.error = err;
-      callback(signingError);
+      callback(new SigningError(err.message));
       return;
     }
 
     if (!credentials.private_key || !credentials.client_email) {
       var errorMessage = [
-        'Signing failed. Could not find a `private_key` or `client_email`.',
+        'Could not find a `private_key` or `client_email`.',
         'Please verify you are authorized with these credentials available.'
       ].join(' ');
 
-      callback(new Error(errorMessage));
+      callback(new SigningError(errorMessage));
       return;
     }
 
diff --git a/package.json b/package.json
index fa2b14c2815..48fd4d6ce62 100644
--- a/package.json
+++ b/package.json
@@ -51,6 +51,7 @@
     "arrify": "^1.0.0",
     "async": "^1.4.2",
     "concat-stream": "^1.5.0",
+    "create-error-class": "^2.0.1",
     "dns-zonefile": "0.1.10",
     "duplexify": "^3.2.0",
     "extend": "^3.0.0",
diff --git a/test/storage/file.js b/test/storage/file.js
index 72af4c0bfd7..62364836c02 100644
--- a/test/storage/file.js
+++ b/test/storage/file.js
@@ -1499,9 +1499,8 @@ describe('File', function() {
       file.getSignedPolicy({
         expires: Date.now() + 5
       }, function(err) {
-        var errorMessage = 'Signing failed. See `error` property.';
-        assert.strictEqual(err.message, errorMessage);
-        assert.strictEqual(err.error, error);
+        assert.strictEqual(err.name, 'SigningError');
+        assert.strictEqual(err.message, error.message);
         done();
       });
     });
@@ -1516,10 +1515,11 @@ describe('File', function() {
         expires: Date.now() + 5
       }, function(err) {
         var errorMessage = [
-          'Signing failed. Could not find a `private_key`.',
+          'Could not find a `private_key`.',
           'Please verify you are authorized with this property available.'
         ].join(' ');
 
+        assert.strictEqual(err.name, 'SigningError');
         assert.strictEqual(err.message, errorMessage);
         done();
       });
@@ -1789,9 +1789,8 @@ describe('File', function() {
         action: 'read',
         expires: Date.now() + 5
       }, function(err) {
-        var errorMessage = 'Signing failed. See `error` property.';
-        assert.strictEqual(err.message, errorMessage);
-        assert.strictEqual(err.error, error);
+        assert.strictEqual(err.name, 'SigningError');
+        assert.strictEqual(err.message, error.message);
         done();
       });
     });
@@ -1807,10 +1806,11 @@ describe('File', function() {
         expires: Date.now() + 5
       }, function(err) {
         var errorMessage = [
-          'Signing failed. Could not find a `private_key` or `client_email`.',
+          'Could not find a `private_key` or `client_email`.',
           'Please verify you are authorized with these credentials available.'
         ].join(' ');
 
+        assert.strictEqual(err.name, 'SigningError');
         assert.strictEqual(err.message, errorMessage);
         done();
       });