diff --git a/src/Umbraco.Tests/Routing/RoutesCacheTests.cs b/src/Umbraco.Tests/Routing/RoutesCacheTests.cs
new file mode 100644
index 0000000000..80bdcb3b7f
--- /dev/null
+++ b/src/Umbraco.Tests/Routing/RoutesCacheTests.cs
@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using NUnit.Framework;
+using Umbraco.Tests.TestHelpers;
+using Umbraco.Web.PublishedCache.XmlPublishedCache;
+
+namespace Umbraco.Tests.Routing
+{
+    [DatabaseTestBehavior(DatabaseBehavior.NewDbFileAndSchemaPerFixture)]
+    [TestFixture]
+    public class RoutesCacheTests : BaseRoutingTest
+    {
+        [Test]
+        public void U4_7939()
+        {
+            //var routingContext = GetRoutingContext("/test", 1111);
+            var umbracoContext = GetUmbracoContext("/test", 0);
+            var cache = umbracoContext.ContentCache.InnerCache as PublishedContentCache;
+            if (cache == null) throw new Exception("Unsupported IPublishedContentCache, only the Xml one is supported.");
+
+            PublishedContentCache.UnitTesting = false; // else does not write to routes cache
+            Assert.IsFalse(PublishedContentCache.UnitTesting);
+
+            var z = cache.GetByRoute(umbracoContext, false, "/home/sub1");
+            Assert.IsNotNull(z);
+            Assert.AreEqual(1173, z.Id);
+
+            var routes = cache.RoutesCache.GetCachedRoutes();
+            Assert.AreEqual(1, routes.Count);
+
+            // before the fix, the following assert would fail because the route would
+            // have been stored as { 0, "/home/sub1" } - essentially meaning we were NOT
+            // storing anything in the route cache!
+
+            Assert.AreEqual(1173, routes.Keys.First());
+            Assert.AreEqual("/home/sub1", routes.Values.First());
+        }
+    }
+}
diff --git a/src/Umbraco.Tests/Umbraco.Tests.csproj b/src/Umbraco.Tests/Umbraco.Tests.csproj
index 2f048f12b5..234591da37 100644
--- a/src/Umbraco.Tests/Umbraco.Tests.csproj
+++ b/src/Umbraco.Tests/Umbraco.Tests.csproj
@@ -193,6 +193,7 @@
     <Compile Include="Persistence\Repositories\TaskRepositoryTest.cs" />
     <Compile Include="Persistence\Repositories\TaskTypeRepositoryTest.cs" />
     <Compile Include="Resolvers\ResolverBaseTest.cs" />
+    <Compile Include="Routing\RoutesCacheTests.cs" />
     <Compile Include="Routing\UrlRoutingTestBase.cs" />
     <Compile Include="Security\UmbracoBackOfficeIdentityTests.cs" />
     <Compile Include="Services\ContentTypeServiceExtensionsTests.cs" />
diff --git a/src/Umbraco.Web/PublishedCache/XmlPublishedCache/PublishedContentCache.cs b/src/Umbraco.Web/PublishedCache/XmlPublishedCache/PublishedContentCache.cs
index 71c27f2bee..d16133f170 100644
--- a/src/Umbraco.Web/PublishedCache/XmlPublishedCache/PublishedContentCache.cs
+++ b/src/Umbraco.Web/PublishedCache/XmlPublishedCache/PublishedContentCache.cs
@@ -57,12 +57,12 @@ namespace Umbraco.Web.PublishedCache.XmlPublishedCache
             if (content != null && preview == false)
             {
                 var domainRootNodeId = route.StartsWith("/") ? -1 : int.Parse(route.Substring(0, route.IndexOf('/')));
-                var iscanon = 
-                    UnitTesting == false 
+                var iscanon =
+                    UnitTesting == false
                     && DomainHelper.ExistsDomainInPath(umbracoContext.Application.Services.DomainService.GetAll(false), content.Path, domainRootNodeId) == false;
                 // and only if this is the canonical url (the one GetUrl would return)
                 if (iscanon)
-                    _routesCache.Store(contentId, route);
+                    _routesCache.Store(content.Id, route);
             }
 
             return content;
@@ -159,7 +159,7 @@ namespace Umbraco.Web.PublishedCache.XmlPublishedCache
             // we add this check - we look for the document matching "/" and if it's not us, then
             // we do not hide the top level path
             // it has to be taken care of in GetByRoute too so if
-            // "/foo" fails (looking for "/*/foo") we try also "/foo". 
+            // "/foo" fails (looking for "/*/foo") we try also "/foo".
             // this does not make much sense anyway esp. if both "/foo/" and "/bar/foo" exist, but
             // that's the way it works pre-4.10 and we try to be backward compat for the time being
             if (node.Parent == null)
@@ -244,8 +244,8 @@ namespace Umbraco.Web.PublishedCache.XmlPublishedCache
 
         private static IPublishedContent ConvertToDocument(XmlNode xmlNode, bool isPreviewing)
 		{
-		    return xmlNode == null 
-                ? null 
+		    return xmlNode == null
+                ? null
                 : (new XmlPublishedContent(xmlNode, isPreviewing)).CreateModel();
 		}
 
@@ -398,7 +398,7 @@ namespace Umbraco.Web.PublishedCache.XmlPublishedCache
                 if (startNodeId > 0)
                 {
 					// if in a domain then use the root node of the domain
-					xpath = string.Format(XPathStringsDefinition.Root + XPathStrings.DescendantDocumentById, startNodeId);                    
+					xpath = string.Format(XPathStringsDefinition.Root + XPathStrings.DescendantDocumentById, startNodeId);
                 }
                 else
                 {
@@ -409,7 +409,7 @@ namespace Umbraco.Web.PublishedCache.XmlPublishedCache
 					// umbraco does not consistently guarantee that sortOrder starts with 0
 					// so the one that we want is the one with the smallest sortOrder
 					// read http://stackoverflow.com/questions/1128745/how-can-i-use-xpath-to-find-the-minimum-value-of-an-attribute-in-a-set-of-elemen
-                    
+
 					// so that one does not work, because min(@sortOrder) maybe 1
 					// xpath = "/root/*[@isDoc and @sortOrder='0']";
 
@@ -453,7 +453,7 @@ namespace Umbraco.Web.PublishedCache.XmlPublishedCache
                     else
                     {
                         xpathBuilder.AppendFormat(XPathStrings.ChildDocumentByUrlName, part);
-                        
+
                     }
                 }