diff --git a/packages/components/CHANGELOG.md b/packages/components/CHANGELOG.md
index 9603d9656d5069..2ca5bec5bf1f9f 100644
--- a/packages/components/CHANGELOG.md
+++ b/packages/components/CHANGELOG.md
@@ -32,6 +32,7 @@
 
 -   ESLint: Stop disabling `react-hooks/exhaustive-deps` rule ([#66324](https://github.com/WordPress/gutenberg/pull/66324)).
 -   `TabPanel`: Add 40px size prop to tab Button ([#66557](https://github.com/WordPress/gutenberg/pull/66557)).
+-   `Panel`: Add 40px size prop to Button ([#66589](https://github.com/WordPress/gutenberg/pull/66589)).
 
 ## 28.10.0 (2024-10-16)
 
diff --git a/packages/components/src/panel/body.tsx b/packages/components/src/panel/body.tsx
index bf6b867dccbf45..ee1121ef04f4cb 100644
--- a/packages/components/src/panel/body.tsx
+++ b/packages/components/src/panel/body.tsx
@@ -116,6 +116,7 @@ const PanelBodyTitle = forwardRef(
 		return (
 			<h2 className="components-panel__body-title">
 				<Button
+					__next40pxDefaultSize
 					className="components-panel__body-toggle"
 					aria-expanded={ isOpened }
 					ref={ ref }
diff --git a/packages/editor/src/components/plugin-post-publish-panel/test/__snapshots__/index.js.snap b/packages/editor/src/components/plugin-post-publish-panel/test/__snapshots__/index.js.snap
index 5a057456d06aca..b144d525374c96 100644
--- a/packages/editor/src/components/plugin-post-publish-panel/test/__snapshots__/index.js.snap
+++ b/packages/editor/src/components/plugin-post-publish-panel/test/__snapshots__/index.js.snap
@@ -10,7 +10,7 @@ exports[`PluginPostPublishPanel renders fill properly 1`] = `
     >
       <button
         aria-expanded="true"
-        class="components-button components-panel__body-toggle"
+        class="components-button components-panel__body-toggle is-next-40px-default-size"
         type="button"
       >
         <span