diff --git a/core/server/utils/cached-image-size-from-url.js b/core/server/utils/cached-image-size-from-url.js
index 3e1a85333c..6499f1dd5e 100644
--- a/core/server/utils/cached-image-size-from-url.js
+++ b/core/server/utils/cached-image-size-from-url.js
@@ -1,8 +1,7 @@
 var Promise = require('bluebird'),
-    sizeOf = require('./image-size'),
+    imageSize = require('./image-size'),
     logging = require('../logging'),
     errors = require('../errors'),
-    getImageSizeFromUrl = sizeOf.getImageSizeFromUrl,
     imageSizeCache = {};
 
 /**
@@ -20,7 +19,7 @@ function getCachedImageSizeFromUrl(url) {
 
     // image size is not in cache
     if (!imageSizeCache[url]) {
-        return getImageSizeFromUrl(url).then(function (res) {
+        return imageSize.getImageSizeFromUrl(url).then(function (res) {
             imageSizeCache[url] = res;
 
             return Promise.resolve(imageSizeCache[url]);
diff --git a/core/test/unit/server_helpers/ghost_head_spec.js b/core/test/unit/server_helpers/ghost_head_spec.js
index 2f77cdab40..081c0cb1f2 100644
--- a/core/test/unit/server_helpers/ghost_head_spec.js
+++ b/core/test/unit/server_helpers/ghost_head_spec.js
@@ -5,6 +5,7 @@ var should = require('should'), // jshint ignore:line
     moment = require('moment'),
     configUtils = require('../../utils/configUtils'),
     helpers = require('../../../server/helpers'),
+    imageSize = require('../../../server/utils/image-size'),
     proxy = require('../../../server/helpers/proxy'),
     settingsCache = proxy.settingsCache,
     api = proxy.api,
@@ -18,9 +19,15 @@ describe('{{ghost_head}} helper', function () {
         configUtils.restore();
     });
 
-    // TODO: stub `getImageDimensions` to make things faster
     beforeEach(function () {
-        sandbox.stub(api.clients, 'read').returns(new Promise.resolve({
+        /**
+         * Each test case here requests the image dimensions.
+         * The image path is e.g. localhost:port/favicon.ico, but no server is running.
+         * If we don't mock the image size utility, we run into lot's of timeouts.
+         */
+        sandbox.stub(imageSize, 'getImageSizeFromUrl').returns(Promise.resolve());
+
+        sandbox.stub(api.clients, 'read').returns(Promise.resolve({
             clients: [
                 {slug: 'ghost-frontend', secret: 'a1bcde23cfe5', status: 'enabled'}
             ]
diff --git a/core/test/unit/utils/cached-image-size-from-url_spec.js b/core/test/unit/utils/cached-image-size-from-url_spec.js
index 2581696b87..33596be958 100644
--- a/core/test/unit/utils/cached-image-size-from-url_spec.js
+++ b/core/test/unit/utils/cached-image-size-from-url_spec.js
@@ -3,7 +3,7 @@ var should = require('should'),
     Promise = require('bluebird'),
     rewire = require('rewire'),
 
-// Stuff we are testing
+    // Stuff we are testing
     getCachedImageSizeFromUrl = rewire('../../../server/utils/cached-image-size-from-url'),
 
     sandbox = sinon.sandbox.create();
@@ -30,7 +30,7 @@ describe('getCachedImageSizeFromUrl', function () {
             type: 'jpg'
         }));
 
-        getCachedImageSizeFromUrl.__set__('getImageSizeFromUrl', sizeOfStub);
+        getCachedImageSizeFromUrl.__set__('imageSize.getImageSizeFromUrl', sizeOfStub);
 
         getCachedImageSizeFromUrl(url).then(function () {
             // first call to get result from `getImageSizeFromUrl`
@@ -61,7 +61,7 @@ describe('getCachedImageSizeFromUrl', function () {
 
         sizeOfStub.returns(new Promise.reject('error'));
 
-        getCachedImageSizeFromUrl.__set__('getImageSizeFromUrl', sizeOfStub);
+        getCachedImageSizeFromUrl.__set__('imageSize.getImageSizeFromUrl', sizeOfStub);
 
         getCachedImageSizeFromUrl(url)
             .then(function () {