diff --git a/tests/phpunit/includes/bootstrap.php b/tests/phpunit/includes/bootstrap.php
index d85799a910..4e9a06ed26 100644
--- a/tests/phpunit/includes/bootstrap.php
+++ b/tests/phpunit/includes/bootstrap.php
@@ -22,6 +22,9 @@ if ( !is_readable( $config_file_path ) ) {
 	die( "ERROR: wp-tests-config.php is missing! Please use wp-tests-config-sample.php to create a config file.\n" );
 }
 require_once $config_file_path;
+require_once dirname( __FILE__ ) . '/functions.php';
+
+tests_reset_SERVER();
 
 define( 'WP_TESTS_TABLE_PREFIX', $table_prefix );
 define( 'DIR_TESTDATA', dirname( __FILE__ ) . '/../data' );
@@ -37,12 +40,6 @@ define( 'DISABLE_WP_CRON', true );
 define( 'WP_MEMORY_LIMIT', -1 );
 define( 'WP_MAX_MEMORY_LIMIT', -1 );
 
-$_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.1';
-$_SERVER['HTTP_HOST'] = WP_TESTS_DOMAIN;
-$_SERVER['SERVER_NAME'] = WP_TESTS_DOMAIN;
-$_SERVER['REQUEST_METHOD'] = 'GET';
-$_SERVER['REMOTE_ADDR'] = '127.0.0.1';
-
 $PHP_SELF = $GLOBALS['PHP_SELF'] = $_SERVER['PHP_SELF'] = '/index.php';
 
 if ( "1" == getenv( 'WP_MULTISITE' ) ||
@@ -68,8 +65,6 @@ if ( $multisite ) {
 }
 unset( $multisite );
 
-require_once dirname( __FILE__ ) . '/functions.php';
-
 $GLOBALS['_wp_die_disabled'] = false;
 // Allow tests to override wp_die
 tests_add_filter( 'wp_die_handler', '_wp_die_handler_filter' );
diff --git a/tests/phpunit/includes/functions.php b/tests/phpunit/includes/functions.php
index 1030edee82..e3f51dbef5 100644
--- a/tests/phpunit/includes/functions.php
+++ b/tests/phpunit/includes/functions.php
@@ -1,5 +1,20 @@
 <?php
 
+/**
+ * Resets various `$_SERVER` variables that can get altered during tests.
+ */
+function tests_reset_SERVER() {
+	$_SERVER['HTTP_HOST']       = WP_TESTS_DOMAIN;
+	$_SERVER['REMOTE_ADDR']     = '127.0.0.1';
+	$_SERVER['REQUEST_METHOD']  = 'GET';
+	$_SERVER['SERVER_NAME']     = WP_TESTS_DOMAIN;
+	$_SERVER['SERVER_PORT']     = '80';
+	$_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.1';
+
+	unset( $_SERVER['HTTP_REFERER'] );
+	unset( $_SERVER['HTTPS'] );
+}
+
 // For adding hooks before loading WP
 function tests_add_filter($tag, $function_to_add, $priority = 10, $accepted_args = 1) {
 	global $wp_filter, $merged_filters;
diff --git a/tests/phpunit/includes/install.php b/tests/phpunit/includes/install.php
index d33c1b76de..c62b8b943b 100644
--- a/tests/phpunit/includes/install.php
+++ b/tests/phpunit/includes/install.php
@@ -13,11 +13,7 @@ define( 'WP_INSTALLING', true );
 require_once $config_file_path;
 require_once dirname( __FILE__ ) . '/functions.php';
 
-$_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.1';
-$_SERVER['HTTP_HOST'] = WP_TESTS_DOMAIN;
-$_SERVER['SERVER_NAME'] = WP_TESTS_DOMAIN;
-$_SERVER['REQUEST_METHOD'] = 'GET';
-$_SERVER['REMOTE_ADDR'] = '127.0.0.1';
+tests_reset_SERVER();
 
 $PHP_SELF = $GLOBALS['PHP_SELF'] = $_SERVER['PHP_SELF'] = '/index.php';