diff --git a/lib/compat/wordpress-6.3/theme-previews.php b/lib/compat/wordpress-6.3/theme-previews.php
index 31d684c17cf2a..26153d74878b5 100644
--- a/lib/compat/wordpress-6.3/theme-previews.php
+++ b/lib/compat/wordpress-6.3/theme-previews.php
@@ -107,7 +107,7 @@ function block_theme_activate_nonce() {
 	$nonce_handle = 'switch-theme_' . gutenberg_get_theme_preview_path();
 	?>
 <script type="text/javascript">
-	window.BLOCK_THEME_ACTIVATE_NONCE = '<?php echo wp_create_nonce( $nonce_handle ); ?>';
+	window.WP_BLOCK_THEME_ACTIVATE_NONCE = '<?php echo wp_create_nonce( $nonce_handle ); ?>';
 </script>
 	<?php
 }
diff --git a/packages/edit-site/src/utils/use-activate-theme.js b/packages/edit-site/src/utils/use-activate-theme.js
index 64654318274cd..b476056feb6b0 100644
--- a/packages/edit-site/src/utils/use-activate-theme.js
+++ b/packages/edit-site/src/utils/use-activate-theme.js
@@ -29,7 +29,7 @@ export function useActivateTheme() {
 				'themes.php?action=activate&stylesheet=' +
 				currentlyPreviewingTheme() +
 				'&_wpnonce=' +
-				window.BLOCK_THEME_ACTIVATE_NONCE;
+				window.WP_BLOCK_THEME_ACTIVATE_NONCE;
 			await window.fetch( activationURL );
 			const { wp_theme_preview: themePreview, ...params } =
 				location.params;