diff --git a/Octokit.Tests/OctoKit.Tests-NetCore45.csproj b/Octokit.Tests/OctoKit.Tests-NetCore45.csproj
index 6f584c02..3050eb69 100644
--- a/Octokit.Tests/OctoKit.Tests-NetCore45.csproj
+++ b/Octokit.Tests/OctoKit.Tests-NetCore45.csproj
@@ -109,6 +109,7 @@
     <Compile Include="Exceptions\TwoFactorRequiredExceptionTests.cs" />
     <Compile Include="Helpers\NSubstituteExtensions.cs" />
     <Compile Include="Helpers\ReflectionExtensions.cs" />
+    <Compile Include="Helpers\UnixTimestampExtensionsTests.cs" />
     <Compile Include="Helpers\UriExtensionsTests.cs" />
     <Compile Include="Http\ApiConnectionTests.cs" />
     <Compile Include="Clients\AuthorizationsClientTests.cs" />
diff --git a/Octokit.Tests/Octokit.Tests-Portable.csproj b/Octokit.Tests/Octokit.Tests-Portable.csproj
index 776fc864..e64b0f27 100644
--- a/Octokit.Tests/Octokit.Tests-Portable.csproj
+++ b/Octokit.Tests/Octokit.Tests-Portable.csproj
@@ -107,6 +107,7 @@
     <Compile Include="Exceptions\TwoFactorRequiredExceptionTests.cs" />
     <Compile Include="Helpers\NSubstituteExtensions.cs" />
     <Compile Include="Helpers\ReflectionExtensions.cs" />
+    <Compile Include="Helpers\UnixTimestampExtensionsTests.cs" />
     <Compile Include="Helpers\UriExtensionsTests.cs" />
     <Compile Include="Http\ApiConnectionTests.cs" />
     <Compile Include="Clients\AuthorizationsClientTests.cs" />