diff --git a/README.md b/README.md
index da17996..9676bc0 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 # ActivityPub #
 **Contributors:** [automattic](https://profiles.wordpress.org/automattic/), [pfefferle](https://profiles.wordpress.org/pfefferle/), [mediaformat](https://profiles.wordpress.org/mediaformat/), [mattwiebe](https://profiles.wordpress.org/mattwiebe/), [akirk](https://profiles.wordpress.org/akirk/), [jeherve](https://profiles.wordpress.org/jeherve/), [nuriapena](https://profiles.wordpress.org/nuriapena/), [cavalierlife](https://profiles.wordpress.org/cavalierlife/)  
 **Tags:** OStatus, fediverse, activitypub, activitystream  
-**Requires at least:** 4.7  
+**Requires at least:** 5.5  
 **Tested up to:** 6.4  
 **Stable tag:** 1.3.0  
 **Requires PHP:** 5.6  
diff --git a/includes/class-activitypub.php b/includes/class-activitypub.php
index 8b2a405..16d417c 100644
--- a/includes/class-activitypub.php
+++ b/includes/class-activitypub.php
@@ -389,7 +389,7 @@ class Activitypub {
 	 * @return void
 	 */
 	private static function register_post_types() {
-		register_post_type(
+		\register_post_type(
 			Followers::POST_TYPE,
 			array(
 				'labels'           => array(
@@ -406,7 +406,7 @@ class Activitypub {
 			)
 		);
 
-		register_post_meta(
+		\register_post_meta(
 			Followers::POST_TYPE,
 			'activitypub_inbox',
 			array(
@@ -416,7 +416,7 @@ class Activitypub {
 			)
 		);
 
-		register_post_meta(
+		\register_post_meta(
 			Followers::POST_TYPE,
 			'activitypub_errors',
 			array(
@@ -432,7 +432,7 @@ class Activitypub {
 			)
 		);
 
-		register_post_meta(
+		\register_post_meta(
 			Followers::POST_TYPE,
 			'activitypub_user_id',
 			array(
@@ -444,7 +444,7 @@ class Activitypub {
 			)
 		);
 
-		register_post_meta(
+		\register_post_meta(
 			Followers::POST_TYPE,
 			'activitypub_actor_json',
 			array(
@@ -456,7 +456,7 @@ class Activitypub {
 			)
 		);
 
-		do_action( 'activitypub_after_register_post_type' );
+		\do_action( 'activitypub_after_register_post_type' );
 	}
 
 	/**
diff --git a/includes/compat.php b/includes/compat.php
index d1047df..8c274c8 100644
--- a/includes/compat.php
+++ b/includes/compat.php
@@ -76,3 +76,24 @@ if ( ! function_exists( 'array_is_list' ) ) {
 		return true;
 	}
 }
+
+if ( ! function_exists( 'str_contains' ) ) {
+	/**
+	 * Polyfill for `str_contains()` function added in PHP 8.0.
+	 *
+	 * Performs a case-sensitive check indicating if needle is
+	 * contained in haystack.
+	 *
+	 * @param string $haystack The string to search in.
+	 * @param string $needle   The substring to search for in the `$haystack`.
+	 *
+	 * @return bool True if `$needle` is in `$haystack`, otherwise false.
+	 */
+	function str_contains( $haystack, $needle ) {
+		if ( '' === $needle ) {
+			return true;
+		}
+
+		return false !== strpos( $haystack, $needle );
+	}
+}
diff --git a/readme.txt b/readme.txt
index f31f3ab..be92893 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,7 +1,7 @@
 === ActivityPub ===
 Contributors: automattic, pfefferle, mediaformat, mattwiebe, akirk, jeherve, nuriapena, cavalierlife
 Tags: OStatus, fediverse, activitypub, activitystream
-Requires at least: 4.7
+Requires at least: 5.5
 Tested up to: 6.4
 Stable tag: 1.3.0
 Requires PHP: 5.6