diff --git a/OpenXmlFormats/NPOI.OpenXmlFormats.Core.csproj b/OpenXmlFormats/NPOI.OpenXmlFormats.Core.csproj
index 74a1ae5fe..afbbed643 100644
--- a/OpenXmlFormats/NPOI.OpenXmlFormats.Core.csproj
+++ b/OpenXmlFormats/NPOI.OpenXmlFormats.Core.csproj
@@ -1,11 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
 	<GenerateAssemblyInfo>false</GenerateAssemblyInfo>
 	<AssemblyName>NPOI.OpenXmlFormats</AssemblyName>
 	<SignAssembly>true</SignAssembly>
 	<AssemblyOriginatorKeyFile>npoi.snk</AssemblyOriginatorKeyFile>
+	<TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
diff --git a/main/NPOI.Core.csproj b/main/NPOI.Core.csproj
index d0585953b..aecdf1e3f 100644
--- a/main/NPOI.Core.csproj
+++ b/main/NPOI.Core.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
 	<GenerateAssemblyInfo>false</GenerateAssemblyInfo>
 	<AssemblyName>NPOI</AssemblyName>
 	<RootNamespace>NPOI</RootNamespace>
@@ -10,6 +9,7 @@
 	<PackageId>NPOI</PackageId>
 	<RepositoryUrl>https://github.com/tonyqus/npoi</RepositoryUrl>
   <OutputPath>..\solution\Lib</OutputPath>
+  <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
   </PropertyGroup>
 
  
diff --git a/main/SS/Formula/Eval/FunctionEval.cs b/main/SS/Formula/Eval/FunctionEval.cs
index 78ce65505..7e2b6fbe4 100644
--- a/main/SS/Formula/Eval/FunctionEval.cs
+++ b/main/SS/Formula/Eval/FunctionEval.cs
@@ -125,7 +125,7 @@ private static Function[] ProduceFunctions()
             retval[26] = NumericFunction.SIGN; // SIGN
             retval[27] = NumericFunction.ROUND; // ROUND
             retval[28] = new Lookup(); // LOOKUP
-            retval[29] = new Index(); // INDEX
+            retval[29] = new NPOI.SS.Formula.Functions.Index(); // INDEX
             retval[30] = new Rept(); // REPT
             retval[31] = TextFunction.MID; // MID
             retval[32] = TextFunction.LEN; // LEN
diff --git a/ooxml/NPOI.OOXML.Core.csproj b/ooxml/NPOI.OOXML.Core.csproj
index c84ab6001..df2ec5789 100644
--- a/ooxml/NPOI.OOXML.Core.csproj
+++ b/ooxml/NPOI.OOXML.Core.csproj
@@ -1,12 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
 	<GenerateAssemblyInfo>false</GenerateAssemblyInfo>
 	<AssemblyName>NPOI.OOXML</AssemblyName>
 	<RootNamespace>NPOI.OOXML</RootNamespace>
 	<SignAssembly>true</SignAssembly>
 	<AssemblyOriginatorKeyFile>npoi.snk</AssemblyOriginatorKeyFile>
+	<TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
diff --git a/openxml4Net/NPOI.OpenXml4Net.Core.csproj b/openxml4Net/NPOI.OpenXml4Net.Core.csproj
index 09d2997dc..17d77e518 100644
--- a/openxml4Net/NPOI.OpenXml4Net.Core.csproj
+++ b/openxml4Net/NPOI.OpenXml4Net.Core.csproj
@@ -1,11 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
 	<GenerateAssemblyInfo>false</GenerateAssemblyInfo>
 	<AssemblyName>NPOI.OpenXml4Net</AssemblyName>
 	<SignAssembly>true</SignAssembly>
 	<AssemblyOriginatorKeyFile>npoi.snk</AssemblyOriginatorKeyFile>
+	<TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">