diff --git a/lib/client-assets.php b/lib/client-assets.php
index 2296400659880..fb42a2aff3d1e 100644
--- a/lib/client-assets.php
+++ b/lib/client-assets.php
@@ -850,48 +850,58 @@ function gutenberg_enqueue_registered_block_scripts_and_styles() {
  * @since 2.9.0
  */
 function gutenberg_enqueue_theme_block_styles() {
-	$is_editor = ( 'enqueue_block_editor_assets' === current_action() );
+	$is_editor                     = 'enqueue_block_editor_assets' === current_action();
+	$core_block_style_dependencies = $is_editor ?
+		array( 'wp-core-blocks', 'wp-edit-blocks' ) :
+		array( 'wp-core-blocks' );
+	$block_registry                = WP_Block_Type_Registry::get_instance();
 
-	$block_registry         = WP_Block_Type_Registry::get_instance();
-	$block_themes_directory = get_template_directory() . '/blocks/';
-	$block_themes_uri       = get_template_directory_uri() . '/blocks/';
-
-	if (
-		file_exists( $block_themes_directory ) && (
-		$block_themes_handle = opendir( $block_themes_directory )
-	) ) {
-		$core_block_style_dependencies = $is_editor ?
-			array( 'wp-core-blocks', 'wp-edit-blocks' ) :
-			array( 'wp-core-blocks' );
-
-		while ( $filename = readdir( $block_themes_handle ) ) {
-			if (
-				is_file( $block_themes_directory . $filename ) &&
-				pathinfo( $filename, PATHINFO_EXTENSION ) === 'css'
-			) {
-				$block_name         = str_replace( '.', '/', pathinfo( $filename, PATHINFO_FILENAME ) );
-				$block_type         = $block_registry->get_registered( $block_name );
-				$block_style_handle = 'theme-block-style-' . $block_name;
-				$block_style_uri    = $block_themes_uri . $filename;
-
-				if ( $block_type ) {
-					$theme_style_dependencies = array();
-
-					if ( ! empty( $block_type->style ) ) {
-						$theme_style_dependencies += $block_type->style;
-					}
+	// Add child theme first to give precedence over parent theme.
+	$theme_directories = array( get_stylesheet_directory() => get_stylesheet_directory_uri() );
 
-					if ( $is_editor && ! empty( $block_style->editor_style ) ) {
-						$theme_style_dependencies += $block_type->editor_style;
-					}
+	if ( get_template_directory() !== get_stylesheet_directory() ) {
+		$theme_directories[ get_template_directory() ] = get_template_directory_uri();
+	}
 
-					wp_enqueue_style(
-						$block_style_handle, $block_style_uri, $theme_style_dependencies
-					);
-				} elseif ( preg_match( '/^core\//', $block_name ) ) {
-					wp_enqueue_style(
-						$block_style_handle, $block_style_uri, $core_block_style_dependencies
-					);
+	foreach ( $theme_directories as $directory => $directory_uri ) {
+		$block_themes_directory = $directory . '/blocks/';
+		$block_themes_uri       = $directory_uri . '/blocks/';
+
+		if (
+			file_exists( $block_themes_directory ) && (
+			$block_themes_handle = opendir( $block_themes_directory )
+		) ) {
+			while ( $filename = readdir( $block_themes_handle ) ) {
+				if (
+					is_file( $block_themes_directory . $filename ) &&
+					pathinfo( $filename, PATHINFO_EXTENSION ) === 'css'
+				) {
+					$block_name         = str_replace( '.', '/', pathinfo( $filename, PATHINFO_FILENAME ) );
+					$block_type         = $block_registry->get_registered( $block_name );
+					$block_style_handle = 'theme-block-style-' . $block_name;
+					$block_style_uri    = $block_themes_uri . $filename;
+
+					if ( ! wp_style_is( $block_style_handle ) ) {
+						if ( $block_type ) {
+							$theme_style_dependencies = array();
+
+							if ( ! empty( $block_type->style ) ) {
+								$theme_style_dependencies += $block_type->style;
+							}
+
+							if ( $is_editor && ! empty( $block_style->editor_style ) ) {
+								$theme_style_dependencies += $block_type->editor_style;
+							}
+
+							wp_enqueue_style(
+								$block_style_handle, $block_style_uri, $theme_style_dependencies
+							);
+						} elseif ( preg_match( '/^core\//', $block_name ) ) {
+							wp_enqueue_style(
+								$block_style_handle, $block_style_uri, $core_block_style_dependencies
+							);
+						}
+					}
 				}
 			}
 		}