diff --git a/src/MyNihongo.LinqAsync.csproj b/src/MyNihongo.LinqAsync.csproj
index 1f966a3..f77eaf6 100644
--- a/src/MyNihongo.LinqAsync.csproj
+++ b/src/MyNihongo.LinqAsync.csproj
@@ -20,7 +20,7 @@
 	</PropertyGroup>
 
 	<ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
-		<PackageReference Include="System.Collections.Immutable" Version="8.0.0" />
+		<PackageReference Include="System.Collections.Immutable" Version="9.0.0" />
 	</ItemGroup>
 
 	<ItemGroup>