diff --git a/LiteDB.Shell/LiteDB.Shell.csproj b/LiteDB.Shell/LiteDB.Shell.csproj
index af93887d3..f0b30da47 100644
--- a/LiteDB.Shell/LiteDB.Shell.csproj
+++ b/LiteDB.Shell/LiteDB.Shell.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
    <PropertyGroup Condition=" '$(OS)' != 'Windows_NT' ">
      <TargetFrameworks>netcoreapp2.0</TargetFrameworks>
diff --git a/LiteDB/Engine/Services/CacheService.cs b/LiteDB/Engine/Services/CacheService.cs
index 9ff8112aa..ca8f467ab 100644
--- a/LiteDB/Engine/Services/CacheService.cs
+++ b/LiteDB/Engine/Services/CacheService.cs
@@ -1,11 +1,18 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
+
+#if !NET35
+using System.Collections.Concurrent;
+#endif
 
 namespace LiteDB
 {
     internal class CacheService
     {
+
+#if NET35
         /// <summary>
         /// Collection to store clean only pages in cache
         /// </summary>
@@ -15,6 +22,17 @@ internal class CacheService
         /// Collection to store dirty only pages in cache. If page was in _clean, remove from there and insert here
         /// </summary>
         private Dictionary<uint, BasePage> _dirty = new Dictionary<uint, BasePage>();
+#else
+        /// <summary>
+        /// Collection to store clean only pages in cache
+        /// </summary>
+        private ConcurrentDictionary<uint, BasePage> _clean = new ConcurrentDictionary<uint, BasePage>();
+
+        /// <summary>
+        /// Collection to store dirty only pages in cache. If page was in _clean, remove from there and insert here
+        /// </summary>
+        private ConcurrentDictionary<uint, BasePage> _dirty = new ConcurrentDictionary<uint, BasePage>();
+#endif
 
         private IDiskService _disk;
         private Logger _log;
@@ -58,7 +76,11 @@ public void AddPage(BasePage page)
         /// </summary>
         public void SetDirty(BasePage page)
         {
+#if NET35
             _clean.Remove(page.PageID);
+#else
+            _clean.TryRemove(page.PageID, out _);
+#endif
             page.IsDirty = true;
             _dirty[page.PageID] = page;
         }
@@ -114,11 +136,8 @@ public void MarkDirtyAsClean()
         /// </summary>
         public void ClearPages()
         {
-            lock(_clean)
-            {
-                _log.Write(Logger.CACHE, "cleaning cache");
-                _clean.Clear();
-            }
+            _log.Write(Logger.CACHE, "cleaning cache");
+            _clean.Clear();
         }
     }
-}
\ No newline at end of file
+}
diff --git a/LiteDB/LiteDB.csproj b/LiteDB/LiteDB.csproj
index d3e245ddb..7c5242767 100644
--- a/LiteDB/LiteDB.csproj
+++ b/LiteDB/LiteDB.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup Condition=" '$(OS)' != 'Windows_NT' ">
     <TargetFrameworks>netstandard1.3;netstandard2.0</TargetFrameworks>