diff --git a/src/Orchard.Web/Modules/Orchard.ContentTypes/Controllers/AdminController.cs b/src/Orchard.Web/Modules/Orchard.ContentTypes/Controllers/AdminController.cs
index f8f14580f..defebd540 100644
--- a/src/Orchard.Web/Modules/Orchard.ContentTypes/Controllers/AdminController.cs
+++ b/src/Orchard.Web/Modules/Orchard.ContentTypes/Controllers/AdminController.cs
@@ -284,11 +284,14 @@ namespace Orchard.ContentTypes.Controllers {
             if (typeViewModel == null)
                 return HttpNotFound();
 
+            var typePartNames = new HashSet<string>(typeViewModel.Parts.Select(tvm => tvm.PartDefinition.Name));
+
             var viewModel = new AddPartsViewModel {
                 Type = typeViewModel,
                 PartSelections = _contentDefinitionService.GetParts(false/*metadataPartsOnly*/)
-                    .Where(cpd => !typeViewModel.Parts.Any(p => p.PartDefinition.Name == cpd.Name) && cpd.Settings.GetModel<ContentPartSettings>().Attachable)
-                    .Select(cpd => new PartSelectionViewModel { PartName = cpd.Name, PartDisplayName = cpd.DisplayName, PartDescription = cpd.Description})
+                    .Where(cpd => !typePartNames.Contains(cpd.Name) && cpd.Settings.GetModel<ContentPartSettings>().Attachable)
+                    .Select(cpd => new PartSelectionViewModel { PartName = cpd.Name, PartDisplayName = cpd.DisplayName, PartDescription = cpd.Description })
+                    .ToList()
             };
 
             return View(viewModel);
diff --git a/src/Orchard.Web/Modules/Orchard.ContentTypes/Services/ContentDefinitionService.cs b/src/Orchard.Web/Modules/Orchard.ContentTypes/Services/ContentDefinitionService.cs
index 8db21adb0..9e3052c1a 100644
--- a/src/Orchard.Web/Modules/Orchard.ContentTypes/Services/ContentDefinitionService.cs
+++ b/src/Orchard.Web/Modules/Orchard.ContentTypes/Services/ContentDefinitionService.cs
@@ -180,22 +180,30 @@ namespace Orchard.ContentTypes.Services {
         }
 
         public IEnumerable<EditPartViewModel> GetParts(bool metadataPartsOnly) {
-            var typeNames = GetTypes().Select(ctd => ctd.Name);
+            var typeNames = new HashSet<string>(GetTypes().Select(ctd => ctd.Name));
 
             // user-defined parts
             // except for those parts with the same name as a type (implicit type's part or a mistake)
-            var userContentParts = _contentDefinitionManager
-                .ListPartDefinitions()
+            var userContentParts = _contentDefinitionManager.ListPartDefinitions()
                 .Where(cpd => !typeNames.Contains(cpd.Name))
-                .Select(cpd => new EditPartViewModel(cpd));
+                .Select(cpd => new EditPartViewModel(cpd))
+                .ToDictionary(
+                    k => k.Name,
+                    v => v);
 
             // code-defined parts
-            var codeDefinedParts = metadataPartsOnly ? 
-                Enumerable.Empty<EditPartViewModel>() : 
-                _contentPartDrivers.SelectMany(d => d.GetPartInfo().Where(cpd => !userContentParts.Any(m => m.Name == cpd.PartName)).Select(cpi => new EditPartViewModel { Name = cpi.PartName }));
+            var codeDefinedParts = metadataPartsOnly
+                ? Enumerable.Empty<EditPartViewModel>()
+                : _contentPartDrivers
+                    .SelectMany(d => d.GetPartInfo()
+                        .Where(cpd => !userContentParts.ContainsKey(cpd.PartName))
+                        .Select(cpi => new EditPartViewModel { Name = cpi.PartName, DisplayName = cpi.PartName }))
+                    .ToList();
 
             // Order by display name
-            return userContentParts.Union(codeDefinedParts).OrderBy(m => m.DisplayName);
+            return codeDefinedParts
+                .Union(userContentParts.Values)
+                .OrderBy(m => m.DisplayName);
         }
 
         public EditPartViewModel GetPart(string name) {