diff --git a/core/server/web/shared/middlewares/custom-redirects.js b/core/server/web/shared/middlewares/custom-redirects.js
index 58b2412b57..ea13d48ee7 100644
--- a/core/server/web/shared/middlewares/custom-redirects.js
+++ b/core/server/web/shared/middlewares/custom-redirects.js
@@ -17,77 +17,90 @@ const _private = {};
 
 let customRedirectsRouter;
 
-_private.registerRoutes = () => {
+/**
+ *
+ * @param {Object} redirects valid redirects JSON
+ * @returns {Object} instance of express.Router express router handling redirects based on config
+ */
+_private.registerRoutes = (redirects) => {
     debug('redirects loading');
 
-    customRedirectsRouter = express.Router('redirects');
+    const redirectsRouter = express.Router('redirects');
 
-    try {
-        const redirects = redirectsService.loadRedirectsFile();
+    if (labsService.isSet('offers')) {
+        redirects.unshift({
+            from: '/zimo50',
+            to: '/#/portal/offers/abcdefuckoff'
+        });
+    }
 
-        if (labsService.isSet('offers')) {
-            redirects.unshift({
-                from: '/zimo50',
-                to: '/#/portal/offers/abcdefuckoff'
-            });
+    redirects.forEach((redirect) => {
+        /**
+         * Detect case insensitive modifier when regex is enclosed by
+         * / ... /i
+         */
+        let options = '';
+        if (redirect.from.match(/^\/.*\/i$/)) {
+            redirect.from = redirect.from.slice(1, -2);
+            options = 'i';
         }
 
+        /**
+         * always delete trailing slashes, doesn't matter if regex or not
+         * Example:
+         *   - you define /my-blog-post-1/ as from property
+         *   - /my-blog-post-1 or /my-blog-post-1/ should work
+         */
+
+        if (redirect.from.match(/\/$/)) {
+            redirect.from = redirect.from.slice(0, -1);
+        }
+
+        if (redirect.from[redirect.from.length - 1] !== '$') {
+            redirect.from += '/?$';
+        }
+
+        debug('register', redirect.from);
+        redirectsRouter.get(new RegExp(redirect.from, options), function (req, res) {
+            const maxAge = redirect.permanent ? config.get('caching:customRedirects:maxAge') : 0;
+            const toURL = url.parse(redirect.to);
+            const toURLParams = querystring.parse(toURL.query);
+            const currentURL = url.parse(req.url);
+            const currentURLParams = querystring.parse(currentURL.query);
+            const params = Object.assign({}, currentURLParams, toURLParams);
+            const search = querystring.stringify(params);
+
+            toURL.pathname = currentURL.pathname.replace(new RegExp(redirect.from, options), toURL.pathname);
+            toURL.search = search !== '' ? `?${search}` : null;
+
+            /**
+             * Only if the URL is internal should we prepend the Ghost subdirectory
+             * @see https://github.com/TryGhost/Ghost/issues/10776
+             */
+            if (!toURL.hostname) {
+                toURL.pathname = urlUtils.urlJoin(urlUtils.getSubdir(), toURL.pathname);
+            }
+
+            res.set({
+                'Cache-Control': `public, max-age=${maxAge}`
+            });
+
+            res.redirect(redirect.permanent ? 301 : 302, url.format(toURL));
+        });
+    });
+
+    debug('redirects loaded');
+
+    return redirectsRouter;
+};
+
+const loadRoutes = () => {
+    try {
+        const redirects = redirectsService.loadRedirectsFile();
         redirectsService.validate(redirects);
 
-        redirects.forEach((redirect) => {
-            /**
-             * Detect case insensitive modifier when regex is enclosed by
-             * / ... /i
-             */
-            let options = '';
-            if (redirect.from.match(/^\/.*\/i$/)) {
-                redirect.from = redirect.from.slice(1, -2);
-                options = 'i';
-            }
-
-            /**
-             * always delete trailing slashes, doesn't matter if regex or not
-             * Example:
-             *   - you define /my-blog-post-1/ as from property
-             *   - /my-blog-post-1 or /my-blog-post-1/ should work
-             */
-
-            if (redirect.from.match(/\/$/)) {
-                redirect.from = redirect.from.slice(0, -1);
-            }
-
-            if (redirect.from[redirect.from.length - 1] !== '$') {
-                redirect.from += '/?$';
-            }
-
-            debug('register', redirect.from);
-            customRedirectsRouter.get(new RegExp(redirect.from, options), function (req, res) {
-                const maxAge = redirect.permanent ? config.get('caching:customRedirects:maxAge') : 0;
-                const toURL = url.parse(redirect.to);
-                const toURLParams = querystring.parse(toURL.query);
-                const currentURL = url.parse(req.url);
-                const currentURLParams = querystring.parse(currentURL.query);
-                const params = Object.assign({}, currentURLParams, toURLParams);
-                const search = querystring.stringify(params);
-
-                toURL.pathname = currentURL.pathname.replace(new RegExp(redirect.from, options), toURL.pathname);
-                toURL.search = search !== '' ? `?${search}` : null;
-
-                /**
-                 * Only if the URL is internal should we prepend the Ghost subdirectory
-                 * @see https://github.com/TryGhost/Ghost/issues/10776
-                 */
-                if (!toURL.hostname) {
-                    toURL.pathname = urlUtils.urlJoin(urlUtils.getSubdir(), toURL.pathname);
-                }
-
-                res.set({
-                    'Cache-Control': `public, max-age=${maxAge}`
-                });
-
-                res.redirect(redirect.permanent ? 301 : 302, url.format(toURL));
-            });
-        });
+        const redirectsRouter = _private.registerRoutes(redirects);
+        customRedirectsRouter = redirectsRouter;
     } catch (err) {
         if (errors.utils.isIgnitionError(err)) {
             logging.error(err);
@@ -100,8 +113,6 @@ _private.registerRoutes = () => {
             }));
         }
     }
-
-    debug('redirects loaded');
 };
 
 /**
@@ -110,7 +121,7 @@ _private.registerRoutes = () => {
  * - file loads synchronously, because we need to register the routes before anything else
  */
 exports.use = function use(siteApp) {
-    _private.registerRoutes();
+    loadRoutes();
 
     // Recommended approach by express, see https://github.com/expressjs/express/issues/2596#issuecomment-81353034.
     // As soon as the express router get's re-instantiated, the old router instance is not used anymore.
@@ -120,5 +131,5 @@ exports.use = function use(siteApp) {
 };
 
 exports.reload = function reload() {
-    _private.registerRoutes();
+    loadRoutes();
 };
diff --git a/test/regression/api/canary/admin/redirects.test.js b/test/regression/api/canary/admin/redirects.test.js
index b750d211f7..6040cc1172 100644
--- a/test/regression/api/canary/admin/redirects.test.js
+++ b/test/regression/api/canary/admin/redirects.test.js
@@ -383,21 +383,6 @@ describe('Redirects API', function () {
         });
     });
 
-    // https://github.com/TryGhost/Ghost/issues/10898
-    describe('Merge querystring', function () {
-        it('toURL param takes precedence, other params pass through', function () {
-            return startGhost({forceStart: true, redirectsFileExt: '.json'})
-                .then(function () {
-                    return request
-                        .get('/test-params/?q=123&lang=js')
-                        .expect(301)
-                        .then(function (res) {
-                            res.headers.location.should.eql('/result?q=abc&lang=js');
-                        });
-                });
-        });
-    });
-
     // TODO: For backward compatibility, we only check if download, upload endpoints work here.
     // when updating to v4, the old endpoints should be updated to the new ones.
     // And the tests below should be removed.
diff --git a/test/regression/api/v3/admin/redirects.test.js b/test/regression/api/v3/admin/redirects.test.js
index 3e8b302fd7..a975dc8838 100644
--- a/test/regression/api/v3/admin/redirects.test.js
+++ b/test/regression/api/v3/admin/redirects.test.js
@@ -383,21 +383,6 @@ describe('Redirects API', function () {
         });
     });
 
-    // https://github.com/TryGhost/Ghost/issues/10898
-    describe('Merge querystring', function () {
-        it('toURL param takes precedence, other params pass through', function () {
-            return startGhost({forceStart: true, redirectsFileExt: '.json'})
-                .then(function () {
-                    return request
-                        .get('/test-params/?q=123&lang=js')
-                        .expect(301)
-                        .then(function (res) {
-                            res.headers.location.should.eql('/result?q=abc&lang=js');
-                        });
-                });
-        });
-    });
-
     // TODO: For backward compatibility, we only check if download, upload endpoints work here.
     // when updating to v4, the old endpoints should be updated to the new ones.
     // And the tests below should be removed.
diff --git a/test/unit/web/shared/middleware/custom-redirects.test.js b/test/unit/web/shared/middleware/custom-redirects.test.js
new file mode 100644
index 0000000000..6ecf840d78
--- /dev/null
+++ b/test/unit/web/shared/middleware/custom-redirects.test.js
@@ -0,0 +1,48 @@
+const should = require('should');
+const sinon = require('sinon');
+const rewire = require('rewire');
+
+const customRedirects = rewire('../../../../../core/server/web/shared/middlewares/custom-redirects');
+const registerRoutes = customRedirects.__get__('_private.registerRoutes');
+
+describe('UNIT: custom redirects', function () {
+    let res;
+    let req;
+    let next;
+
+    beforeEach(function () {
+        req = {
+            method: 'GET'
+        };
+        res = {
+            redirect: sinon.spy(),
+            set: sinon.spy()
+        };
+
+        next = sinon.spy();
+    });
+
+    afterEach(function () {
+        sinon.restore();
+    });
+
+    // Related to: https://github.com/TryGhost/Ghost/issues/10898
+    it('toURL param takes precedence, other params pass through', function () {
+        const redirectsConfig = [{
+            permanent: true,
+            from: '/test-params',
+            to: '/result?q=abc'
+        }];
+        const redirect = registerRoutes(redirectsConfig);
+
+        req.url = '/test-params/?q=123&lang=js';
+        redirect(req, res, next);
+
+        next.called.should.be.false();
+        res.redirect.called.should.be.true();
+        res.redirect.calledWith(301, '/result?q=abc&lang=js').should.be.true();
+        res.set.calledWith({
+            'Cache-Control': `public, max-age=0`
+        });
+    });
+});