diff --git a/AwsCryptographyPrimitives/runtimes/net/Crypto.csproj b/AwsCryptographyPrimitives/runtimes/net/Crypto.csproj
index f6348d583..ac19c2581 100644
--- a/AwsCryptographyPrimitives/runtimes/net/Crypto.csproj
+++ b/AwsCryptographyPrimitives/runtimes/net/Crypto.csproj
@@ -66,7 +66,7 @@
       System.Collections.Immutable can be removed once dafny.msbuild is updated with
       https://github.com/dafny-lang/dafny.msbuild/pull/10 and versioned
     -->
-    <PackageReference Include="System.Collections.Immutable" Version="1.7.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="9.0.0" />
     <!-- Work around for dafny-lang/dafny/issues/1951; remove once resolved -->
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
 
diff --git a/AwsCryptographyPrimitives/runtimes/net/tests/Test-Crypto.csproj b/AwsCryptographyPrimitives/runtimes/net/tests/Test-Crypto.csproj
index bf7d59dc9..12593beee 100644
--- a/AwsCryptographyPrimitives/runtimes/net/tests/Test-Crypto.csproj
+++ b/AwsCryptographyPrimitives/runtimes/net/tests/Test-Crypto.csproj
@@ -15,7 +15,7 @@
       System.Collections.Immutable can be removed once dafny.msbuild is updated with
       https://github.com/dafny-lang/dafny.msbuild/pull/10 and versioned
     -->
-    <PackageReference Include="System.Collections.Immutable" Version="1.7.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="9.0.0" />
     <!-- Work around for dafny-lang/dafny/issues/1951; remove once resolved -->
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
   </ItemGroup>
diff --git a/StandardLibrary/runtimes/net/STD.csproj b/StandardLibrary/runtimes/net/STD.csproj
index 22a34f9c3..877a374ea 100644
--- a/StandardLibrary/runtimes/net/STD.csproj
+++ b/StandardLibrary/runtimes/net/STD.csproj
@@ -61,7 +61,7 @@
       System.Collections.Immutable can be removed once dafny.msbuild is updated with
       https://github.com/dafny-lang/dafny.msbuild/pull/10 and versioned
     -->
-    <PackageReference Include="System.Collections.Immutable" Version="1.7.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="9.0.0" />
     <!-- Work around for dafny-lang/dafny/issues/1951; remove once resolved -->
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
     <Compile Include="..\..\..\libraries\src\FileIO\FileIO.cs">