diff --git a/src/Umbraco.Core/Models/Stylesheet.cs b/src/Umbraco.Core/Models/Stylesheet.cs
index 7381da0930..586c5915b2 100644
--- a/src/Umbraco.Core/Models/Stylesheet.cs
+++ b/src/Umbraco.Core/Models/Stylesheet.cs
@@ -33,11 +33,11 @@ namespace Umbraco.Core.Models
                 //re-parse it so we can check what properties are different and adjust the event handlers
                 var parsed = StylesheetHelper.ParseRules(Content).ToArray();
                 var names = parsed.Select(x => x.Name).ToArray();
-                var existing = _properties.Value.Where(x => names.Contains(x.Name)).ToArray();
+                var existing = _properties.Value.Where(x => names.InvariantContains(x.Name)).ToArray();
                 //update existing
                 foreach (var stylesheetProperty in existing)
                 {
-                    var updateFrom = parsed.Single(x => x.Name == stylesheetProperty.Name);
+                    var updateFrom = parsed.Single(x => x.Name.InvariantEquals(stylesheetProperty.Name));
                     //remove current event handler while we update, we'll reset it after
                     stylesheetProperty.PropertyChanged -= Property_PropertyChanged;
                     stylesheetProperty.Alias = updateFrom.Selector;
@@ -46,14 +46,14 @@ namespace Umbraco.Core.Models
                     stylesheetProperty.PropertyChanged += Property_PropertyChanged;
                 }
                 //remove no longer existing
-                var nonExisting = _properties.Value.Where(x => names.Contains(x.Name) == false).ToArray();
+                var nonExisting = _properties.Value.Where(x => names.InvariantContains(x.Name) == false).ToArray();
                 foreach (var stylesheetProperty in nonExisting)
                 {
                     stylesheetProperty.PropertyChanged -= Property_PropertyChanged;
                     _properties.Value.Remove(stylesheetProperty);
                 }
                 //add new ones
-                var newItems = parsed.Where(x => _properties.Value.Select(p => p.Name).Contains(x.Name) == false);
+                var newItems = parsed.Where(x => _properties.Value.Select(p => p.Name).InvariantContains(x.Name) == false);
                 foreach (var stylesheetRule in newItems)
                 {
                     var prop = new StylesheetProperty(stylesheetRule.Name, stylesheetRule.Selector, stylesheetRule.Styles);
@@ -128,7 +128,7 @@ namespace Umbraco.Core.Models
         /// <param name="property"></param>
         public void AddProperty(StylesheetProperty property)
         {
-            if (Properties.Any(x => x.Name == property.Name))
+            if (Properties.Any(x => x.Name.InvariantEquals(property.Name)))
             {
                 throw new DuplicateNameException("The property with the name " + property.Name + " already exists in the collection");
             }
@@ -151,7 +151,7 @@ namespace Umbraco.Core.Models
         /// <param name="name"></param>
         public void RemoveProperty(string name)
         {
-            if (Properties.Any(x => x.Name == name))
+            if (Properties.Any(x => x.Name.InvariantEquals(name)))
             {
                 Content = StylesheetHelper.ReplaceRule(Content, name, null);
             }
diff --git a/src/Umbraco.Tests/Persistence/Repositories/StylesheetRepositoryTest.cs b/src/Umbraco.Tests/Persistence/Repositories/StylesheetRepositoryTest.cs
index dcbab3dd88..87182e4ad0 100644
--- a/src/Umbraco.Tests/Persistence/Repositories/StylesheetRepositoryTest.cs
+++ b/src/Umbraco.Tests/Persistence/Repositories/StylesheetRepositoryTest.cs
@@ -1,4 +1,5 @@
-using System.IO;
+using System.Data;
+using System.IO;
 using System.Linq;
 using System.Text;
 using Moq;
@@ -118,6 +119,26 @@ p{font-size:2em;}"));
             Assert.AreEqual(1, stylesheet.Properties.Count());
         }
 
+        [Test]
+        public void Throws_When_Adding_Duplicate_Properties()
+        {
+            // Arrange
+            var provider = new FileUnitOfWorkProvider();
+            var unitOfWork = provider.GetUnitOfWork();
+
+            var repository = new StylesheetRepository(unitOfWork, _fileSystem);
+
+            // Act
+            var stylesheet = new Stylesheet("test-update.css") { Content = "body { color:#000; } .bold {font-weight:bold;}" };
+            repository.AddOrUpdate(stylesheet);
+            unitOfWork.Commit();
+
+            stylesheet.AddProperty(new StylesheetProperty("Test", "p", "font-size:2em;"));
+
+            Assert.Throws<DuplicateNameException>(() => stylesheet.AddProperty(new StylesheetProperty("test", "p", "font-size:2em;")));
+
+        }
+
         [Test]
         public void Can_Perform_Delete()
         {
diff --git a/src/Umbraco.Web/umbraco.presentation/umbraco/settings/stylesheet/property/EditStyleSheetProperty.aspx.cs b/src/Umbraco.Web/umbraco.presentation/umbraco/settings/stylesheet/property/EditStyleSheetProperty.aspx.cs
index 75471cd676..f058b31bb7 100644
--- a/src/Umbraco.Web/umbraco.presentation/umbraco/settings/stylesheet/property/EditStyleSheetProperty.aspx.cs
+++ b/src/Umbraco.Web/umbraco.presentation/umbraco/settings/stylesheet/property/EditStyleSheetProperty.aspx.cs
@@ -45,7 +45,7 @@ namespace umbraco.cms.presentation.settings.stylesheet
 
             var propName = IsPostBack ? OriginalName.Value : Request.QueryString["prop"];
 
-            _stylesheetproperty = _sheet.Properties.FirstOrDefault(x => x.Name == propName);
+            _stylesheetproperty = _sheet.Properties.FirstOrDefault(x => x.Name.InvariantEquals(propName));
             if (_stylesheetproperty == null) throw new InvalidOperationException("No stylesheet property found with name: " + Request.QueryString["prop"]);
 
             Panel1.Text = ui.Text("stylesheet", "editstylesheetproperty", UmbracoUser);