diff --git a/packages/components/CHANGELOG.md b/packages/components/CHANGELOG.md
index db8b0f749217f..1e94853763cd3 100644
--- a/packages/components/CHANGELOG.md
+++ b/packages/components/CHANGELOG.md
@@ -26,6 +26,7 @@
 ### Internal
 
 -   `SlotFill`: rewrite the non-portal version to use `observableMap` ([#67400](https://github.com/WordPress/gutenberg/pull/67400)).
+-   `DatePicker`: Prepare day buttons for 40px default size ([#68156](https://github.com/WordPress/gutenberg/pull/68156)).
 
 ## 29.0.0 (2024-12-11)
 
diff --git a/packages/components/src/date-time/date/index.tsx b/packages/components/src/date-time/date/index.tsx
index ca093f9d70847..e7afcccf249dc 100644
--- a/packages/components/src/date-time/date/index.tsx
+++ b/packages/components/src/date-time/date/index.tsx
@@ -306,6 +306,7 @@ function Day( {
 
 	return (
 		<DayButton
+			__next40pxDefaultSize
 			ref={ ref }
 			className="components-datetime__date__day" // Unused, for backwards compatibility.
 			disabled={ isInvalid }