diff --git a/src/wp-admin/includes/upgrade.php b/src/wp-admin/includes/upgrade.php
index 9c4cb43580..63580cceb0 100644
--- a/src/wp-admin/includes/upgrade.php
+++ b/src/wp-admin/includes/upgrade.php
@@ -512,7 +512,7 @@ function wp_install_maybe_enable_pretty_permalinks() {
 		 * can block head requests.
 		 */
 		$response          = wp_remote_get( $test_url, array( 'timeout' => 5 ) );
-		$x_pingback_header = wp_remote_retrieve_header( $response, 'X-Pingback' );
+		$x_pingback_header = wp_remote_retrieve_header( $response, 'x-pingback' );
 		$pretty_permalinks = $x_pingback_header && get_bloginfo( 'pingback_url' ) === $x_pingback_header;
 
 		if ( $pretty_permalinks ) {
diff --git a/tests/phpunit/tests/functions/doEnclose.php b/tests/phpunit/tests/functions/doEnclose.php
index 4d1a2ee818..e907f179df 100644
--- a/tests/phpunit/tests/functions/doEnclose.php
+++ b/tests/phpunit/tests/functions/doEnclose.php
@@ -271,8 +271,8 @@ class Tests_Functions_DoEnclose extends WP_UnitTestCase {
 			),
 			'ogg' => array(
 				'headers' => array(
-					'content-length' => 321,
-					'content-type'   => 'audio/ogg',
+					'Content-Length' => 321,
+					'Content-Type'   => 'audio/ogg',
 				),
 			),
 		);