diff --git a/packages/block-library/src/pattern/index.php b/packages/block-library/src/pattern/index.php
index 1f5477968b92d1..f05bb333bd186d 100644
--- a/packages/block-library/src/pattern/index.php
+++ b/packages/block-library/src/pattern/index.php
@@ -44,7 +44,6 @@ function render_block_core_pattern( $attributes ) {
 	// Backward compatibility for handling Block Hooks and injecting the theme attribute in the Gutenberg plugin.
 	// This can be removed when the minimum supported WordPress is >= 6.4.
 	if ( defined( 'IS_GUTENBERG_PLUGIN' ) && IS_GUTENBERG_PLUGIN && ! function_exists( 'traverse_and_serialize_blocks' ) ) {
-		$content = _inject_theme_attribute_in_block_template_content( $content );
 		$blocks  = parse_blocks( $content );
 		$content = gutenberg_serialize_blocks( $blocks );
 	}
diff --git a/packages/block-library/src/template-part/index.php b/packages/block-library/src/template-part/index.php
index a7bd4033affc34..3ad400906945b8 100644
--- a/packages/block-library/src/template-part/index.php
+++ b/packages/block-library/src/template-part/index.php
@@ -18,13 +18,10 @@ function render_block_core_template_part( $attributes ) {
 	$template_part_id = null;
 	$content          = null;
 	$area             = WP_TEMPLATE_PART_AREA_UNCATEGORIZED;
+	$theme            = isset( $attributes['theme'] ) ? $attributes['theme'] : get_stylesheet();
 
-	if (
-		isset( $attributes['slug'] ) &&
-		isset( $attributes['theme'] ) &&
-		get_stylesheet() === $attributes['theme']
-	) {
-		$template_part_id    = $attributes['theme'] . '//' . $attributes['slug'];
+	if ( isset( $attributes['slug'] ) && get_stylesheet() === $theme ) {
+		$template_part_id    = $theme . '//' . $attributes['slug'];
 		$template_part_query = new WP_Query(
 			array(
 				'post_type'           => 'wp_template_part',
@@ -34,7 +31,7 @@ function render_block_core_template_part( $attributes ) {
 					array(
 						'taxonomy' => 'wp_theme',
 						'field'    => 'name',
-						'terms'    => $attributes['theme'],
+						'terms'    => $theme,
 					),
 				),
 				'posts_per_page'      => 1,