diff --git a/src/Umbraco.Core/Collections/ConcurrentHashSet.cs b/src/Umbraco.Core/Collections/ConcurrentHashSet.cs
index 0424c4dae1..c4dba51acd 100644
--- a/src/Umbraco.Core/Collections/ConcurrentHashSet.cs
+++ b/src/Umbraco.Core/Collections/ConcurrentHashSet.cs
@@ -1,8 +1,8 @@
 using System;
 using System.Collections;
-using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 
 namespace Umbraco.Core.Collections
 {
@@ -14,10 +14,9 @@ namespace Umbraco.Core.Collections
     [Serializable]
     public class ConcurrentHashSet<T> : ICollection<T>
     {
-        // Internally we just use a ConcurrentDictionary with the same value for the Value (since we don't actually care about the value)
-        private static readonly byte _emptyValue = 0x0;
-        private readonly ConcurrentDictionary<T, byte> _innerSet = new ConcurrentDictionary<T, byte>();
-        
+        private readonly HashSet<T> _innerSet = new HashSet<T>();
+        private readonly ReaderWriterLockSlim _instanceLocker = new ReaderWriterLockSlim(LockRecursionPolicy.NoRecursion);
+
         /// <summary>
         /// Returns an enumerator that iterates through the collection.
         /// </summary>
@@ -27,7 +26,7 @@ namespace Umbraco.Core.Collections
         /// <filterpriority>1</filterpriority>
         public IEnumerator<T> GetEnumerator()
         {
-            return _innerSet.Keys.GetEnumerator();
+            return GetThreadSafeClone().GetEnumerator();
         }
 
         /// <summary>
@@ -51,7 +50,16 @@ namespace Umbraco.Core.Collections
         /// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</exception>
         public bool Remove(T item)
         {
-            return _innerSet.TryRemove(item, out _);
+            try
+            {
+                _instanceLocker.EnterWriteLock();
+                return _innerSet.Remove(item);
+            }
+            finally
+            {
+                if (_instanceLocker.IsWriteLockHeld)
+                    _instanceLocker.ExitWriteLock();
+            }
         }
 
 
@@ -66,7 +74,17 @@ namespace Umbraco.Core.Collections
         {
             get
             {
-                return _innerSet.Count;
+                try
+                {
+                    _instanceLocker.EnterReadLock();
+                    return _innerSet.Count;
+                }
+                finally
+                {
+                    if (_instanceLocker.IsReadLockHeld)
+                        _instanceLocker.ExitReadLock();
+                }
+
             }
         }
 
@@ -81,10 +99,19 @@ namespace Umbraco.Core.Collections
         /// <summary>
         /// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
         /// </summary>
-        /// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
+        /// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</exception>
         public void Add(T item)
         {
-            _innerSet.TryAdd(item, _emptyValue);
+            try
+            {
+                _instanceLocker.EnterWriteLock();
+                _innerSet.Add(item);
+            }
+            finally
+            {
+                if (_instanceLocker.IsWriteLockHeld)
+                    _instanceLocker.ExitWriteLock();
+            }
         }
 
         /// <summary>
@@ -94,7 +121,21 @@ namespace Umbraco.Core.Collections
         /// <returns></returns>
         public bool TryAdd(T item)
         {
-            return _innerSet.TryAdd(item, _emptyValue);
+            if (Contains(item)) return false;
+            try
+            {
+                _instanceLocker.EnterWriteLock();
+
+                //double check
+                if (_innerSet.Contains(item)) return false;
+                _innerSet.Add(item);
+                return true;
+            }
+            finally
+            {
+                if (_instanceLocker.IsWriteLockHeld)
+                    _instanceLocker.ExitWriteLock();
+            }
         }
 
         /// <summary>
@@ -103,7 +144,16 @@ namespace Umbraco.Core.Collections
         /// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only. </exception>
         public void Clear()
         {
-            _innerSet.Clear();
+            try
+            {
+                _instanceLocker.EnterWriteLock();
+                _innerSet.Clear();
+            }
+            finally
+            {
+                if (_instanceLocker.IsWriteLockHeld)
+                    _instanceLocker.ExitWriteLock();
+            }
         }
 
         /// <summary>
@@ -115,7 +165,16 @@ namespace Umbraco.Core.Collections
         /// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
         public bool Contains(T item)
         {
-            return _innerSet.ContainsKey(item);
+            try
+            {
+                _instanceLocker.EnterReadLock();
+                return _innerSet.Contains(item);
+            }
+            finally
+            {
+                if (_instanceLocker.IsReadLockHeld)
+                    _instanceLocker.ExitReadLock();
+            }
         }
 
         /// <summary>
@@ -124,8 +183,24 @@ namespace Umbraco.Core.Collections
         /// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from the <see cref="T:System.Collections.Concurrent.IProducerConsumerCollection`1"/>. The array must have zero-based indexing.</param><param name="index">The zero-based index in <paramref name="array"/> at which copying begins.</param><exception cref="T:System.ArgumentNullException"><paramref name="array"/> is a null reference (Nothing in Visual Basic).</exception><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="index"/> is less than zero.</exception><exception cref="T:System.ArgumentException"><paramref name="index"/> is equal to or greater than the length of the <paramref name="array"/> -or- The number of elements in the source <see cref="T:System.Collections.Concurrent.ConcurrentQueue`1"/> is greater than the available space from <paramref name="index"/> to the end of the destination <paramref name="array"/>.</exception>
         public void CopyTo(T[] array, int index)
         {
-            var keys = _innerSet.Keys;
-            keys.CopyTo(array, index);
+            var clone = GetThreadSafeClone();
+            clone.CopyTo(array, index);
+        }
+
+        private HashSet<T> GetThreadSafeClone()
+        {
+            HashSet<T> clone = null;
+            try
+            {
+                _instanceLocker.EnterReadLock();
+                clone = new HashSet<T>(_innerSet, _innerSet.Comparer);
+            }
+            finally
+            {
+                if (_instanceLocker.IsReadLockHeld)
+                    _instanceLocker.ExitReadLock();
+            }
+            return clone;
         }
 
         /// <summary>
@@ -134,8 +209,8 @@ namespace Umbraco.Core.Collections
         /// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from <see cref="T:System.Collections.ICollection"/>. The <see cref="T:System.Array"/> must have zero-based indexing. </param><param name="index">The zero-based index in <paramref name="array"/> at which copying begins. </param><exception cref="T:System.ArgumentNullException"><paramref name="array"/> is null. </exception><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="index"/> is less than zero. </exception><exception cref="T:System.ArgumentException"><paramref name="array"/> is multidimensional.-or- The number of elements in the source <see cref="T:System.Collections.ICollection"/> is greater than the available space from <paramref name="index"/> to the end of the destination <paramref name="array"/>. </exception><exception cref="T:System.ArgumentException">The type of the source <see cref="T:System.Collections.ICollection"/> cannot be cast automatically to the type of the destination <paramref name="array"/>. </exception><filterpriority>2</filterpriority>
         public void CopyTo(Array array, int index)
         {
-            var keys = _innerSet.Keys;
-            Array.Copy(keys.ToArray(), 0, array, index, keys.Count);
+            var clone = GetThreadSafeClone();
+            Array.Copy(clone.ToArray(), 0, array, index, clone.Count);
         }
     }
 }
diff --git a/src/umbraco.sln.DotSettings b/src/umbraco.sln.DotSettings
index 3d42d188af..bd8ca8b974 100644
--- a/src/umbraco.sln.DotSettings
+++ b/src/umbraco.sln.DotSettings
@@ -1,4 +1,5 @@
 <wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EdotCover_002EIde_002ECore_002EFilterManagement_002EModel_002ESolutionFilterSettingsManagerMigrateSettings/@EntryIndexedValue">True</s:Boolean>
 	<s:String x:Key="/Default/FilterSettingsManager/CoverageFilterXml/@EntryValue">&lt;data&gt;&lt;IncludeFilters /&gt;&lt;ExcludeFilters /&gt;&lt;/data&gt;</s:String>
 	<s:String x:Key="/Default/FilterSettingsManager/AttributeFilterXml/@EntryValue">&lt;data /&gt;</s:String>
 	<s:String x:Key="/Default/PatternsAndTemplates/StructuralSearch/Pattern/=2DA32DA040A7D74599ABE288C7224CF0/Comment/@EntryValue">Disposable construction</s:String>