diff --git a/src/core/Elsa.Abstractions/Builders/ISetupActivity.cs b/src/core/Elsa.Abstractions/Builders/ISetupActivity.cs
index feb282e7b..3f36f2d8a 100644
--- a/src/core/Elsa.Abstractions/Builders/ISetupActivity.cs
+++ b/src/core/Elsa.Abstractions/Builders/ISetupActivity.cs
@@ -13,7 +13,7 @@ namespace Elsa.Builders
     public interface ISetupActivity<T> : ISetupActivity where T : IActivity
     {
         ISetupActivity<T> Set<TProperty>(Expression<Func<T, TProperty>> propertyAccessor,
-            Func<ActivityExecutionContext, ValueTask<object?>> valueFactory);
+            Func<ActivityExecutionContext, ValueTask<TProperty?>> valueFactory);
     }
 
     public static class SetupActivityExtensions