diff --git a/wp-includes/load.php b/wp-includes/load.php
index 7c9c2e7757..fe97810ae5 100644
--- a/wp-includes/load.php
+++ b/wp-includes/load.php
@@ -13,7 +13,7 @@
  * @return string The HTTP protocol. Default: HTTP/1.0.
  */
 function wp_get_server_protocol() {
-	$protocol = $_SERVER['SERVER_PROTOCOL'];
+	$protocol = isset( $_SERVER['SERVER_PROTOCOL'] ) ? $_SERVER['SERVER_PROTOCOL'] : '';
 	if ( ! in_array( $protocol, array( 'HTTP/1.1', 'HTTP/2', 'HTTP/2.0' ) ) ) {
 		$protocol = 'HTTP/1.0';
 	}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index a601674b05..5496c05942 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45399';
+$wp_version = '5.3-alpha-45400';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.