diff --git a/src/wp-includes/blocks.php b/src/wp-includes/blocks.php
index 4d3a34e34f..6fc72e358a 100644
--- a/src/wp-includes/blocks.php
+++ b/src/wp-includes/blocks.php
@@ -150,8 +150,8 @@ function register_block_script_handle( $metadata, $field_name, $index = 0 ) {
 	 * Determine if the block script was registered in a theme, by checking if the script path starts with either
 	 * the parent (template) or child (stylesheet) directory path.
 	 */
-	$is_parent_theme_block = str_starts_with( $script_path_norm, $template_path_norm );
-	$is_child_theme_block  = str_starts_with( $script_path_norm, $stylesheet_path_norm );
+	$is_parent_theme_block = str_starts_with( $script_path_norm, trailingslashit( $template_path_norm ) );
+	$is_child_theme_block  = str_starts_with( $script_path_norm, trailingslashit( $stylesheet_path_norm ) );
 	$is_theme_block        = ( $is_parent_theme_block || $is_child_theme_block );
 
 	$script_uri = '';
@@ -270,8 +270,8 @@ function register_block_style_handle( $metadata, $field_name, $index = 0 ) {
 
 		// Determine if the block style was registered in a theme, by checking if the script path starts with either
 		// the parent (template) or child (stylesheet) directory path.
-		$is_parent_theme_block = str_starts_with( $style_path_norm, $template_path_norm );
-		$is_child_theme_block  = str_starts_with( $style_path_norm, $stylesheet_path_norm );
+		$is_parent_theme_block = str_starts_with( $style_path_norm, trailingslashit( $template_path_norm ) );
+		$is_child_theme_block  = str_starts_with( $style_path_norm, trailingslashit( $stylesheet_path_norm ) );
 		$is_theme_block        = ( $is_parent_theme_block || $is_child_theme_block );
 
 		if ( $is_core_block ) {
diff --git a/tests/phpunit/tests/blocks/register.php b/tests/phpunit/tests/blocks/register.php
index 0a5047c6d1..8ad1a88f3a 100644
--- a/tests/phpunit/tests/blocks/register.php
+++ b/tests/phpunit/tests/blocks/register.php
@@ -270,6 +270,21 @@ class Tests_Blocks_Register extends WP_UnitTestCase {
 		$result   = register_block_script_handle( $metadata, 'script' );
 
 		$this->assertSame( 'unit-tests-test-block-script', $result );
+
+		// Test the behavior directly within the unit test
+		$this->assertFalse(
+			strpos(
+				wp_normalize_path( realpath( dirname( $metadata['file'] ) . '/' . $metadata['script'] ) ),
+				trailingslashit( wp_normalize_path( get_template_directory() ) )
+			) === 0
+		);
+
+		$this->assertFalse(
+			strpos(
+				wp_normalize_path( realpath( dirname( $metadata['file'] ) . '/' . $metadata['script'] ) ),
+				trailingslashit( wp_normalize_path( get_stylesheet_directory() ) )
+			) === 0
+		);
 	}
 
 	/**
@@ -438,6 +453,21 @@ class Tests_Blocks_Register extends WP_UnitTestCase {
 			wp_normalize_path( realpath( DIR_TESTDATA . '/blocks/notice/block.css' ) ),
 			wp_normalize_path( wp_styles()->get_data( 'unit-tests-test-block-style', 'path' ) )
 		);
+
+		// Test the behavior directly within the unit test
+		$this->assertFalse(
+			strpos(
+				wp_normalize_path( realpath( dirname( $metadata['file'] ) . '/' . $metadata['style'] ) ),
+				trailingslashit( wp_normalize_path( get_template_directory() ) )
+			) === 0
+		);
+
+		$this->assertFalse(
+			strpos(
+				wp_normalize_path( realpath( dirname( $metadata['file'] ) . '/' . $metadata['style'] ) ),
+				trailingslashit( wp_normalize_path( get_stylesheet_directory() ) )
+			) === 0
+		);
 	}
 
 	/**