diff --git a/src/DIT.Workflower/Query.cs b/src/DIT.Workflower/Query.cs
index 0b071ab..f17509f 100644
--- a/src/DIT.Workflower/Query.cs
+++ b/src/DIT.Workflower/Query.cs
@@ -2,6 +2,8 @@ namespace DIT.Workflower;
 
 
 public sealed class ListTransitionsRequest<TState, TCommand, TContext>
+    where TState : struct
+    where TCommand : struct
 {
     public TState? From { get; set; }