diff --git a/includes/functions.php b/includes/functions.php
index d1b7991..31d29cf 100644
--- a/includes/functions.php
+++ b/includes/functions.php
@@ -300,7 +300,7 @@ function get_blacklist() {
 	$blacklist_hosts  = \explode( PHP_EOL, $blacklist );
 
 	// if no values have been set, revert to the defaults
-	if ( ! $blacklist || ! $blacklist_hosts || ! is_array( $blacklist_hosts ) ) {
+	if ( ! $blacklist || ! $blacklist_hosts || ! \is_array( $blacklist_hosts ) ) {
 		$blacklist_hosts = array(
 			'gab.com',
 		);
diff --git a/includes/rest/class-inbox.php b/includes/rest/class-inbox.php
index 3709d4e..baca644 100644
--- a/includes/rest/class-inbox.php
+++ b/includes/rest/class-inbox.php
@@ -126,7 +126,7 @@ class Inbox {
 			'required' => true,
 			'type' => 'string',
 			'validate_callback' => function( $param, $request, $key ) {
-				if ( ! is_string( $param ) ) {
+				if ( ! \is_string( $param ) ) {
 					$param = $param['id'];
 				}
 				return ! \Activitypub\is_blacklisted( $param );
@@ -138,13 +138,13 @@ class Inbox {
 			'required' => true,
 			'type' => array( 'object', 'string' ),
 			'validate_callback' => function( $param, $request, $key ) {
-				if ( ! is_string( $param ) ) {
+				if ( ! \is_string( $param ) ) {
 					$param = $param['id'];
 				}
 				return ! \Activitypub\is_blacklisted( $param );
 			},
 			'sanitize_callback' => function( $param, $request, $key ) {
-				if ( ! is_string( $param ) ) {
+				if ( ! \is_string( $param ) ) {
 					$param = $param['id'];
 				}
 				return \esc_url_raw( $param );
diff --git a/includes/rest/class-server.php b/includes/rest/class-server.php
index 79926fc..841c6ba 100644
--- a/includes/rest/class-server.php
+++ b/includes/rest/class-server.php
@@ -19,7 +19,7 @@ class Server extends \WP_REST_Server {
 		$content_type = $request->get_content_type();
 
 		// check for content-sub-types like 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'
-		if ( preg_match( '/application\/([a-zA-Z+_-]+\+)json/', $content_type['value'] ) ) {
+		if ( \preg_match( '/application\/([a-zA-Z+_-]+\+)json/', $content_type['value'] ) ) {
 			$request->set_header( 'Content-Type', 'application/json' );
 		}