diff --git a/lib/compat/wordpress-6.0/class-gutenberg-rest-pattern-directory-controller.php b/lib/compat/wordpress-6.0/class-gutenberg-rest-pattern-directory-controller.php
index 5f639bd62baa5f..e92b25f675abbd 100644
--- a/lib/compat/wordpress-6.0/class-gutenberg-rest-pattern-directory-controller.php
+++ b/lib/compat/wordpress-6.0/class-gutenberg-rest-pattern-directory-controller.php
@@ -57,16 +57,7 @@ public function get_items( $request ) {
 			$query_args['slug'] = $slug;
 		}
 
-		/**
-		 * Include a hash of the query args, so that different requests are stored in
-		 * separate caches.
-		 *
-		 * MD5 is chosen for its speed, low-collision rate, universal availability, and to stay
-		 * under the character limit for `_site_transient_timeout_{...}` keys.
-		 *
-		 * @link https://stackoverflow.com/questions/3665247/fastest-hash-for-non-cryptographic-uses
-		 */
-		$transient_key = 'wp_remote_block_patterns_' . md5( implode( '-', $query_args ) );
+		$transient_key = $this->get_transient_key( $query_args );
 
 		/**
 		 * Use network-wide transient to improve performance. The locale is the only site
@@ -75,11 +66,7 @@ public function get_items( $request ) {
 		$raw_patterns = get_site_transient( $transient_key );
 
 		if ( ! $raw_patterns ) {
-			$api_url = add_query_arg(
-				array_map( 'rawurlencode', $query_args ),
-				'http://api.wordpress.org/patterns/1.0/'
-			);
-
+			$api_url = 'http://api.wordpress.org/patterns/1.0/?' . build_query( $query_args );
 			if ( wp_http_supports( array( 'ssl' ) ) ) {
 				$api_url = set_url_scheme( $api_url, 'https' );
 			}
@@ -138,4 +125,40 @@ public function get_items( $request ) {
 
 		return new WP_REST_Response( $response );
 	}
+
+	/**
+	 * Include a hash of the query args, so that different requests are stored in
+	 * separate caches.
+	 *
+	 * MD5 is chosen for its speed, low-collision rate, universal availability, and to stay
+	 * under the character limit for `_site_transient_timeout_{...}` keys.
+	 *
+	 * @link https://stackoverflow.com/questions/3665247/fastest-hash-for-non-cryptographic-uses
+	 *
+	 * @since 6.0.0
+	 * @todo This should be removed when the minimum required WordPress version is >= 6.0.
+	 *
+	 * @param array $query_args Query arguments to generate a transient key from.
+	 * @return string Transient key.
+	 */
+	protected function get_transient_key( $query_args ) {
+		if ( method_exists( get_parent_class( $this ), __FUNCTION__ ) ) {
+			return parent::get_transient_key( $query_args );
+		}
+
+		if ( isset( $query_args['slug'] ) ) {
+			// This is an additional precaution because the "sort" function expects an array.
+			$query_args['slug'] = wp_parse_list( $query_args['slug'] );
+
+			// Empty arrays should not affect the transient key.
+			if ( empty( $query_args['slug'] ) ) {
+				unset( $query_args['slug'] );
+			} else {
+				// Sort the array so that the transient key doesn't depend on the order of slugs.
+				sort( $query_args['slug'] );
+			}
+		}
+
+		return 'wp_remote_block_patterns_' . md5( serialize( $query_args ) );
+	}
 }