diff --git a/src/WebSocket.Rx.UnitTests/WebSocket.Rx.UnitTests.csproj b/src/WebSocket.Rx.UnitTests/WebSocket.Rx.UnitTests.csproj
index 7bad6aa..79212d6 100644
--- a/src/WebSocket.Rx.UnitTests/WebSocket.Rx.UnitTests.csproj
+++ b/src/WebSocket.Rx.UnitTests/WebSocket.Rx.UnitTests.csproj
@@ -11,7 +11,7 @@
 
     <ItemGroup>
         <PackageReference Include="Microsoft.Testing.Extensions.CodeCoverage" Version="18.5.2"/>
-        <PackageReference Include="NSubstitute" Version="5.3.0"/>
+        <PackageReference Include="NSubstitute" Version="6.0.0"/>
         <PackageReference Include="xunit.v3.mtp-v2" Version="3.2.2"/>
     </ItemGroup>