diff --git a/wp-includes/class-wp-simplepie-file.php b/wp-includes/class-wp-simplepie-file.php
index 56d3047112..beb40efbcd 100644
--- a/wp-includes/class-wp-simplepie-file.php
+++ b/wp-includes/class-wp-simplepie-file.php
@@ -87,7 +87,7 @@ class WP_SimplePie_File extends SimplePie_File {
 					if ( 'content-type' === $name ) {
 						$this->headers[ $name ] = array_pop( $value );
 					} else {
-						$this->headers[ $name ] = join( ', ', $value );
+						$this->headers[ $name ] = implode( ', ', $value );
 					}
 				}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 175fa6bfb5..31820dd9d5 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.7-alpha-49804';
+$wp_version = '5.7-alpha-49805';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.