diff --git a/imm/Imm.cs b/imm/Imm.cs
index d0dc98a..6978349 100644
--- a/imm/Imm.cs
+++ b/imm/Imm.cs
@@ -101,7 +101,7 @@ public record class Versioned<T> : Imm
 
 	[lib.Dont]
 	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
-	public ChangeDelegate OnChange = (x, y) => {};
+	public ChangeDelegate OnChange = (old, cur) => {};
 
 	public T Process( Func<T, T> fn, string reason = "" )
 	{