diff --git a/Build/MQTTnet.AspNetCore.nuspec b/Build/MQTTnet.AspNetCore.nuspec
index f9bc8a04..e8e01d3b 100644
--- a/Build/MQTTnet.AspNetCore.nuspec
+++ b/Build/MQTTnet.AspNetCore.nuspec
@@ -28,6 +28,14 @@
         <dependency id="MQTTnet" version="$nugetVersion" />
       </group>
     </dependencies>
+    <frameworkReferences>
+      <group targetFramework=".NETCoreApp3.1">
+        <frameworkReference name="Microsoft.AspNetCore.App" />
+      </group>
+      <group targetFramework="net5.0">
+        <frameworkReference name="Microsoft.AspNetCore.App" />
+      </group>
+    </frameworkReferences>
   </metadata>
 
   <files>
diff --git a/Build/MQTTnet.Extensions.ManagedClient.nuspec b/Build/MQTTnet.Extensions.ManagedClient.nuspec
index b6587bfd..b360569a 100644
--- a/Build/MQTTnet.Extensions.ManagedClient.nuspec
+++ b/Build/MQTTnet.Extensions.ManagedClient.nuspec
@@ -35,6 +35,9 @@
     <!-- .NET Standard 2.0 -->
     <file src="..\Source\MQTTnet.Extensions.ManagedClient\bin\Release\netstandard2.0\MQTTnet.Extensions.ManagedClient.*" target="lib\netstandard2.0\" />
 
+    <!-- .NET Standard 2.1 -->
+    <file src="..\Source\MQTTnet.Extensions.ManagedClient\bin\Release\netstandard2.1\MQTTnet.Extensions.ManagedClient.*" target="lib\netstandard2.1\" />
+
     <!-- Universal Windows -->
     <file src="..\Source\MQTTnet.Extensions.ManagedClient\bin\Release\uap10.0\MQTTnet.Extensions.ManagedClient.*" target="lib\uap10.0\" />
 
diff --git a/Build/MQTTnet.Extensions.Rpc.nuspec b/Build/MQTTnet.Extensions.Rpc.nuspec
index 05eb8fa4..283ac11e 100644
--- a/Build/MQTTnet.Extensions.Rpc.nuspec
+++ b/Build/MQTTnet.Extensions.Rpc.nuspec
@@ -35,6 +35,9 @@
     <!-- .NET Standard 2.0 -->
     <file src="..\Source\MQTTnet.Extensions.Rpc\bin\Release\netstandard2.0\MQTTnet.Extensions.Rpc.*" target="lib\netstandard2.0\" />
 
+    <!-- .NET Standard 2.1 -->
+    <file src="..\Source\MQTTnet.Extensions.Rpc\bin\Release\netstandard2.1\MQTTnet.Extensions.Rpc.*" target="lib\netstandard2.1\" />
+
     <!-- Universal Windows -->
     <file src="..\Source\MQTTnet.Extensions.Rpc\bin\Release\uap10.0\MQTTnet.Extensions.Rpc.*" target="lib\uap10.0\" />
 
diff --git a/Build/MQTTnet.Extensions.WebSocket4Net.nuspec b/Build/MQTTnet.Extensions.WebSocket4Net.nuspec
index 7d150148..640b6909 100644
--- a/Build/MQTTnet.Extensions.WebSocket4Net.nuspec
+++ b/Build/MQTTnet.Extensions.WebSocket4Net.nuspec
@@ -15,22 +15,8 @@
     <copyright>Copyright Christian Kratky 2016-2020</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin Blazor</tags>
     <dependencies>
-    <group targetFramework="netstandard1.3">
-        <dependency id="MQTTnet" version="$nugetVersion" />
-        <dependency id="WebSocket4Net" version="0.15.2" />
-      </group>
-      <group targetFramework="netstandard2.0">
-        <dependency id="MQTTnet" version="$nugetVersion" />
-        <dependency id="WebSocket4Net" version="0.15.2" />
-      </group>
-      <group targetFramework="netstandard2.1">
-        <dependency id="MQTTnet" version="$nugetVersion" />
-        <dependency id="WebSocket4Net" version="0.15.2" />
-      </group>
-      <group targetFramework="uap10.0">
-        <dependency id="MQTTnet" version="$nugetVersion" />
-        <dependency id="WebSocket4Net" version="0.15.2" />
-      </group>
+      <dependency id="MQTTnet" version="$nugetVersion" />
+      <dependency id="WebSocket4Net" version="0.15.2" />
     </dependencies>
   </metadata>
 
@@ -50,6 +36,9 @@
     <!-- .NET Standard 2.0 -->
     <file src="..\Source\MQTTnet.Extensions.WebSocket4Net\bin\Release\netstandard2.0\MQTTnet.Extensions.WebSocket4Net.*" target="lib\netstandard2.0\" />
 
+    <!-- .NET Standard 2.1 -->
+    <file src="..\Source\MQTTnet.Extensions.WebSocket4Net\bin\Release\netstandard2.1\MQTTnet.Extensions.WebSocket4Net.*" target="lib\netstandard2.1\" />
+
     <!-- Universal Windows -->
     <file src="..\Source\MQTTnet.Extensions.WebSocket4Net\bin\Release\uap10.0\MQTTnet.Extensions.WebSocket4Net.*" target="lib\uap10.0\" />
 
diff --git a/Build/MQTTnet.nuspec b/Build/MQTTnet.nuspec
index f29fe20a..30d6171d 100644
--- a/Build/MQTTnet.nuspec
+++ b/Build/MQTTnet.nuspec
@@ -22,30 +22,18 @@ Git commit: $gitCommit
     <copyright>Copyright Christian Kratky 2016-2020</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin Blazor</tags>
     <dependencies>
+      <group targetFramework="net452" />
+      <group targetFramework="net461" />
       <group targetFramework="netstandard1.3">
-        <dependency id="NETStandard.Library" version="1.3.0" />
-        <dependency id="System.Net.Security" version="4.3.2" />
-        <dependency id="System.Net.WebSockets" version="4.3.0" />
-        <dependency id="System.Net.WebSockets.Client" version="4.3.2" />
-      </group>
-      <group targetFramework="netstandard2.0">
-        <dependency id="NETStandard.Library" version="2.0.0" />
-        <dependency id="System.Net.Security" version="4.3.2" />
-        <dependency id="System.Net.WebSockets" version="4.3.0" />
-        <dependency id="System.Net.WebSockets.Client" version="4.3.2" />
-      </group>
-      <group targetFramework="netstandard2.1">
-        <dependency id="NETStandard.Library" version="2.0.0" />
-        <dependency id="System.Net.Security" version="4.3.2" />
-        <dependency id="System.Net.WebSockets" version="4.3.0" />
-        <dependency id="System.Net.WebSockets.Client" version="4.3.2" />
-      </group>
-      <group targetFramework="netcoreapp3.1">
-        <dependency id="NETStandard.Library" version="2.0.0" />
+        <dependency id="NETStandard.Library" version="1.6.1" />
         <dependency id="System.Net.Security" version="4.3.2" />
         <dependency id="System.Net.WebSockets" version="4.3.0" />
         <dependency id="System.Net.WebSockets.Client" version="4.3.2" />
       </group>
+      <group targetFramework="netstandard2.0" />
+      <group targetFramework="netstandard2.1" />
+      <group targetFramework="netcoreapp3.1" />
+      <group targetFramework="net5.0" />
       <group targetFramework="uap10.0">
         <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="6.2.10" />
       </group>
diff --git a/Build/build.ps1 b/Build/build.ps1
index 75907bdf..b1d3cc94 100644
--- a/Build/build.ps1
+++ b/Build/build.ps1
@@ -102,7 +102,7 @@ Remove-Item "nuget.exe" -Force -Recurse -ErrorAction SilentlyContinue
 # Build MQTTnet.Server Portable
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion --framework net5.0
 
-$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\publish"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\net5.0\publish"
 $destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Portable-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
@@ -113,7 +113,7 @@ If(Test-path $destination) {Remove-item $destination}
 # Build MQTTnet.Server Linux-x64
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion --self-contained --runtime linux-x64 --framework net5.0
 
-$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\linux-x64\publish"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\net5.0\linux-x64\publish"
 $destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Linux-x64-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
@@ -124,7 +124,7 @@ If(Test-path $destination) {Remove-item $destination}
 # Build MQTTnet.Server Linux-ARM
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion --self-contained --runtime linux-arm --framework net5.0
 
-$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\linux-ARM\publish"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\net5.0\linux-ARM\publish"
 $destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Linux-ARM-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
@@ -135,7 +135,7 @@ If(Test-path $destination) {Remove-item $destination}
 # Build MQTTnet.Server Windows-x64
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion --self-contained --runtime win-x64 --framework net5.0
 
-$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\win-x64\publish"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\net5.0\win-x64\publish"
 $destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Windows-x64-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
diff --git a/Source/MQTTnet/MQTTnet.csproj b/Source/MQTTnet/MQTTnet.csproj
index 42989f38..8efd8727 100644
--- a/Source/MQTTnet/MQTTnet.csproj
+++ b/Source/MQTTnet/MQTTnet.csproj
@@ -35,14 +35,6 @@
   <PropertyGroup Condition="'$(Configuration)'=='Debug'">
     <DebugType>Full</DebugType>
   </PropertyGroup>
-  
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x86'" />
-
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'" />
-
-  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Release|netstandard1.3|AnyCPU'">
-    <DefineConstants>RELEASE;NETSTANDARD1_3</DefineConstants>
-  </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
@@ -54,20 +46,8 @@
     <PackageReference Include="System.Net.WebSockets.Client" Version="4.3.2" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
-    <PackageReference Include="System.Net.Security" Version="4.3.2" />
-    <PackageReference Include="System.Net.WebSockets" Version="4.3.0" />
-    <PackageReference Include="System.Net.WebSockets.Client" Version="4.3.2" />
-  </ItemGroup>
-
   <ItemGroup Condition="'$(TargetFramework)'=='uap10.0'">
     <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.2.10" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)'=='net452'">
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(TargetFramework)'=='net461'">
-  </ItemGroup>
-  
 </Project>
\ No newline at end of file