diff --git a/Octokit.Tests/Octokit.Tests.csproj b/Octokit.Tests/Octokit.Tests.csproj
index 17e333d049..c136242846 100644
--- a/Octokit.Tests/Octokit.Tests.csproj
+++ b/Octokit.Tests/Octokit.Tests.csproj
@@ -31,7 +31,7 @@
   <ItemGroup>
     <ProjectReference Include="..\Octokit\Octokit.csproj" />
     <ProjectReference Include="..\Octokit.Reactive\Octokit.Reactive.csproj" />
-    <PackageReference Include="NSubstitute" Version="3.1.0" />
+    <PackageReference Include="NSubstitute" Version="4.2.1" />
   </ItemGroup>
 
   <PropertyGroup Condition=" '$(TargetFramework)' == 'netcoreapp2.0' ">