diff --git a/src/wp-includes/block-template-utils.php b/src/wp-includes/block-template-utils.php
index b1a3172fbb..f4958050c6 100644
--- a/src/wp-includes/block-template-utils.php
+++ b/src/wp-includes/block-template-utils.php
@@ -503,7 +503,7 @@ function _build_block_template_result_from_file( $template_file, $template_type
 
 	$template                 = new WP_Block_Template();
 	$template->id             = $theme . '//' . $template_file['slug'];
-	$template->theme          = $theme;
+	$template->theme          = ! empty( $template_file['theme'] ) ? $template_file['theme'] : $theme;
 	$template->content        = _inject_theme_attribute_in_block_template_content( $template_content );
 	$template->slug           = $template_file['slug'];
 	$template->source         = 'theme';
diff --git a/tests/phpunit/tests/block-template-utils.php b/tests/phpunit/tests/block-template-utils.php
index 440dbc15d9..a77f7e9d81 100644
--- a/tests/phpunit/tests/block-template-utils.php
+++ b/tests/phpunit/tests/block-template-utils.php
@@ -123,6 +123,25 @@ class Tests_Block_Template_Utils extends WP_UnitTestCase {
 		$this->assertSame( WP_TEMPLATE_PART_AREA_HEADER, $template_part->area );
 	}
 
+	/**
+	 * Tests that _build_block_template_result_from_post() returns the correct theme
+	 * for the template when a child theme is active.
+	 *
+	 * @ticket 55437
+	 *
+	 * @covers ::_build_block_template_result_from_post
+	 */
+	function test_build_block_template_result_from_post_with_child_theme() {
+		switch_theme( 'block-theme-child' );
+
+		$template = _build_block_template_result_from_post(
+			self::$template_post,
+			'wp_template'
+		);
+
+		$this->assertSame( self::TEST_THEME, $template->theme );
+	}
+
 	function test_build_block_template_result_from_file() {
 		$template = _build_block_template_result_from_file(
 			array(
@@ -161,6 +180,29 @@ class Tests_Block_Template_Utils extends WP_UnitTestCase {
 		$this->assertSame( WP_TEMPLATE_PART_AREA_HEADER, $template_part->area );
 	}
 
+	/**
+	 * Tests that _build_block_template_result_from_file() returns the correct theme
+	 * for the template when a child theme is active.
+	 *
+	 * @ticket 55437
+	 *
+	 * @covers ::_build_block_template_result_from_file
+	 */
+	function test_build_block_template_result_from_file_with_child_theme() {
+		switch_theme( 'block-theme-child' );
+
+		$template = _build_block_template_result_from_file(
+			array(
+				'slug'  => 'single',
+				'path'  => __DIR__ . '/../data/templates/template.html',
+				'theme' => self::TEST_THEME,
+			),
+			'wp_template'
+		);
+
+		$this->assertSame( self::TEST_THEME, $template->theme );
+	}
+
 	function test_inject_theme_attribute_in_block_template_content() {
 		$theme                           = get_stylesheet();
 		$content_without_theme_attribute = '<!-- wp:template-part {"slug":"header","align":"full", "tagName":"header","className":"site-header"} /-->';