diff --git a/PulumiTestHelper/Internals/Mocks.cs b/PulumiTestHelper/Internals/Mocks.cs
index 2eac6bf..9a90309 100644
--- a/PulumiTestHelper/Internals/Mocks.cs
+++ b/PulumiTestHelper/Internals/Mocks.cs
@@ -68,9 +68,10 @@ private Dictionary<string, object> GetResourceMocks(MockResourceArgs args)
     private void AddStackReferenceMocks(MockResourceArgs args, ImmutableDictionary<string, object>.Builder outputs)
     {
         var mocks = resourceMocks
-            .Where(x => x is StackReferenceMock)
-            .Where(x => ((StackReferenceMock) x).StackReferenceName == args.Name)
-            .Select(x => x.Mocks).DeepMergeMany();
+            .OfType<StackReferenceMock>()
+            .Where(x => x.StackReferenceName == args.Name)
+            .Select(x => x.Mocks)
+            .DeepMergeMany();
 
         outputs.Add("secretOutputNames", new List<string>());
         outputs.Add("outputs", mocks);
@@ -86,6 +87,4 @@ private Dictionary<string, object> GetCallMocks(MockCallArgs args)
 
         return mocks.DeepMergeInto(mocksFromFunc);
     }
-
-    
 }
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