diff --git a/src/expr/impl/src/aggregate/first_last_value.rs b/src/expr/impl/src/aggregate/first_last_value.rs
index e4577361c6089..841442148f722 100644
--- a/src/expr/impl/src/aggregate/first_last_value.rs
+++ b/src/expr/impl/src/aggregate/first_last_value.rs
@@ -41,15 +41,9 @@ fn first_value(state: &mut FirstValueState, input: Option<ScalarRefImpl<'_>>) {
     }
 }
 
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Clone, Default, EstimateSize)]
 struct FirstValueState(Option<Datum>);
 
-impl EstimateSize for FirstValueState {
-    fn estimated_heap_size(&self) -> usize {
-        self.0.estimated_heap_size()
-    }
-}
-
 impl AggStateDyn for FirstValueState {}
 
 impl From<&FirstValueState> for Datum {