diff --git a/src/ReactiveUI.Validation/ReactiveUI.Validation.csproj b/src/ReactiveUI.Validation/ReactiveUI.Validation.csproj
index b0f03f47..ec7226f5 100644
--- a/src/ReactiveUI.Validation/ReactiveUI.Validation.csproj
+++ b/src/ReactiveUI.Validation/ReactiveUI.Validation.csproj
@@ -12,6 +12,6 @@
   </ItemGroup>
 
   <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard')) or $(TargetFramework.StartsWith('net4'))">
-    <PackageReference Include="System.Collections.Immutable" Version="8.0.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="9.0.0" />
   </ItemGroup>
 </Project>