diff --git a/activitypub.php b/activitypub.php
index f50a4a916..c23e5eb30 100644
--- a/activitypub.php
+++ b/activitypub.php
@@ -29,7 +29,7 @@
 \defined( 'ACTIVITYPUB_SHOW_PLUGIN_RECOMMENDATIONS' ) || \define( 'ACTIVITYPUB_SHOW_PLUGIN_RECOMMENDATIONS', true );
 \defined( 'ACTIVITYPUB_MAX_IMAGE_ATTACHMENTS' ) || \define( 'ACTIVITYPUB_MAX_IMAGE_ATTACHMENTS', 3 );
 \defined( 'ACTIVITYPUB_HASHTAGS_REGEXP' ) || \define( 'ACTIVITYPUB_HASHTAGS_REGEXP', '(?:(?<=\s)|(?<=<p>)|(?<=<br>)|^)#([A-Za-z0-9_]+)(?:(?=\s|[[:punct:]]|$))' );
-\defined( 'ACTIVITYPUB_USERNAME_REGEXP' ) || \define( 'ACTIVITYPUB_USERNAME_REGEXP', '(?:([A-Za-z0-9_-]+)@((?:[A-Za-z0-9_-]+\.)+[A-Za-z]+))' );
+\defined( 'ACTIVITYPUB_USERNAME_REGEXP' ) || \define( 'ACTIVITYPUB_USERNAME_REGEXP', '(?:([A-Za-z0-9\._-]+)@((?:[A-Za-z0-9_-]+\.)+[A-Za-z]+))' );
 \defined( 'ACTIVITYPUB_CUSTOM_POST_CONTENT' ) || \define( 'ACTIVITYPUB_CUSTOM_POST_CONTENT', "<strong>[ap_title]</strong>\n\n[ap_content]\n\n[ap_hashtags]\n\n[ap_shortlink]" );
 \defined( 'ACTIVITYPUB_AUTHORIZED_FETCH' ) || \define( 'ACTIVITYPUB_AUTHORIZED_FETCH', false );
 \defined( 'ACTIVITYPUB_DISABLE_REWRITES' ) || \define( 'ACTIVITYPUB_DISABLE_REWRITES', false );
diff --git a/includes/class-mention.php b/includes/class-mention.php
index 01bbeaf47..0b8c0b5e5 100644
--- a/includes/class-mention.php
+++ b/includes/class-mention.php
@@ -101,7 +101,14 @@ public static function replace_with_links( $result ) {
 			if ( ! empty( $metadata['preferredUsername'] ) ) {
 				$username = $metadata['preferredUsername'];
 			}
-			return \sprintf( '<a rel="mention" class="u-url mention" href="%s">@<span>%s</span></a>', esc_url( $metadata['url'] ), esc_html( $username ) );
+
+			$url = isset( $metadata['url'] ) ? $metadata['url'] : $metadata['url'];
+
+			if ( \is_array( $url ) ) {
+				$url = $url[0];
+			}
+
+			return \sprintf( '<a rel="mention" class="u-url mention" href="%s">@<span>%s</span></a>', esc_url( $url ), esc_html( $username ) );
 		}
 
 		return $result[0];