diff --git a/src/Orchard.Web/Modules/Orchard.Workflows/Orchard.Workflows.csproj b/src/Orchard.Web/Modules/Orchard.Workflows/Orchard.Workflows.csproj
index 13ab0937e..fd05a7a25 100644
--- a/src/Orchard.Web/Modules/Orchard.Workflows/Orchard.Workflows.csproj
+++ b/src/Orchard.Web/Modules/Orchard.Workflows/Orchard.Workflows.csproj
@@ -110,7 +110,6 @@
     <Content Include="Scripts\orchard-workflows.js" />
     <Content Include="Styles\images\menu.workflows.png" />
     <Content Include="Styles\menu.workflows-admin.css" />
-    <Content Include="Styles\workflows-activity.css" />
     <Content Include="Styles\images\cog.png" />
     <Content Include="Styles\workflows-activity-delete.css" />
     <Content Include="Styles\workflows-activity-timer.css" />
diff --git a/src/Orchard.Web/Modules/Orchard.Workflows/ResourceManifest.cs b/src/Orchard.Web/Modules/Orchard.Workflows/ResourceManifest.cs
index 140486403..0d0fdf829 100644
--- a/src/Orchard.Web/Modules/Orchard.Workflows/ResourceManifest.cs
+++ b/src/Orchard.Web/Modules/Orchard.Workflows/ResourceManifest.cs
@@ -1,6 +1,8 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.IO;
-using System.Web;
+using System.Linq;
+using Orchard.Caching;
 using Orchard.Environment;
 using Orchard.Environment.Extensions;
 using Orchard.FileSystems.VirtualPath;
@@ -14,16 +16,19 @@ namespace Orchard.Workflows {
         private readonly IHostEnvironment _hostEnvironment;
         private readonly IExtensionManager _extensionManager;
         private readonly IVirtualPathProvider _virtualPathProvider;
+        private readonly ICacheManager _cacheManager;
 
         public ResourceManifest(
             Work<IActivitiesManager> activitiesManager,
             IHostEnvironment hostEnvironment,
             IExtensionManager extensionManager,
-            IVirtualPathProvider virtualPathProvider) {
+            IVirtualPathProvider virtualPathProvider,
+            ICacheManager cacheManager) {
             _activitiesManager = activitiesManager;
             _hostEnvironment = hostEnvironment;
             _extensionManager = extensionManager;
             _virtualPathProvider = virtualPathProvider;
+            _cacheManager = cacheManager;
         }
 
         public void BuildManifests(ResourceManifestBuilder builder) {
@@ -31,28 +36,44 @@ namespace Orchard.Workflows {
 
             manifest.DefineStyle("WorkflowsAdmin").SetUrl("orchard-workflows-admin.css").SetDependencies("~/Themes/TheAdmin/Styles/Site.css");
 
-            var resourceNames = new List<string>();
+            manifest.DefineScript("jsPlumb").SetUrl("jquery.jsPlumb-1.4.1-all-min.js").SetDependencies("jQueryUI");
 
-            foreach (var activity in _activitiesManager.Value.GetActivities()) {
-                var assemblyName = activity.GetType().Assembly.GetName().Name;
-                var descriptor = _extensionManager.GetExtension(assemblyName);
-                if (descriptor == null) continue;
 
-                var stylesPath = _virtualPathProvider.Combine(descriptor.VirtualPath, "Styles");
-                var resourceName = "WorkflowsActivity-" + activity.Name;
-                var filename = resourceName.HtmlClassify() + ".css";
-                var filePath = _virtualPathProvider.Combine(_hostEnvironment.MapPath(stylesPath), filename);
+            // Trying to find a matching activity CSS for each activity in the extensions they come from.
+            var resourceNamesAndPaths = _cacheManager.Get("Orchard.Workflows.ActivityResourceNames", context => {
+                var resourceNameAndPathList = new List<Tuple<string, string>>();
 
-                if (File.Exists(filePath)) {
-                    resourceNames.Add(resourceName);
+                foreach (var activity in _activitiesManager.Value.GetActivities()) {
+                    var assemblyName = activity.GetType().Assembly.GetName().Name;
+                    var extension = _extensionManager.GetExtension(assemblyName);
+                    if (extension == null) continue;
 
-                    manifest.DefineStyle(resourceName).SetUrl(filename).SetDependencies("WorkflowsAdmin");
+                    var stylesPath = _virtualPathProvider.Combine(extension.VirtualPath, "Styles");
+                    var resourceName = "WorkflowsActivity-" + activity.Name;
+                    var filename = resourceName.HtmlClassify() + ".css";
+                    var filePath = _virtualPathProvider.Combine(_hostEnvironment.MapPath(stylesPath), filename);
+
+                    if (File.Exists(filePath)) {
+                        /* Since stylesheets are shapes, we don't need to create the resource with the full path to the CSS file,
+                         * because extensions can override those shapes by file name if they reference Orchard.Workflows,
+                         * even when they don't exist in Orchard.Workflows. */
+                        resourceNameAndPathList.Add(Tuple.Create(resourceName, filename));
+                    }
                 }
+
+                return resourceNameAndPathList;
+            });
+
+            foreach (var resourceNameAndPath in resourceNamesAndPaths) {
+                manifest
+                    .DefineStyle(resourceNameAndPath.Item1)
+                    .SetUrl(resourceNameAndPath.Item2)
+                    .SetDependencies("WorkflowsAdmin");
             }
 
-            manifest.DefineStyle("WorkflowsActivities").SetUrl("workflows-activity.css").SetDependencies(resourceNames.ToArray());
-
-            manifest.DefineScript("jsPlumb").SetUrl("jquery.jsPlumb-1.4.1-all-min.js").SetDependencies("jQueryUI");
+            manifest
+                .DefineStyle("WorkflowsActivities")
+                .SetDependencies(resourceNamesAndPaths.Select(resourceNameAndPath => resourceNameAndPath.Item1).ToArray());
         }
     }
 }
diff --git a/src/Orchard.Web/Modules/Orchard.Workflows/Styles/workflows-activity.css b/src/Orchard.Web/Modules/Orchard.Workflows/Styles/workflows-activity.css
deleted file mode 100644
index 5f282702b..000000000
--- a/src/Orchard.Web/Modules/Orchard.Workflows/Styles/workflows-activity.css
+++ /dev/null
@@ -1 +0,0 @@
-
\ No newline at end of file