diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index a9f0e6ed8d..07b0f6a208 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -690,16 +690,14 @@ function switch_theme( $stylesheet ) {
 
 	$nav_menu_locations = get_theme_mod( 'nav_menu_locations' );
 
-	$old_theme  = wp_get_theme();
-	$new_theme = wp_get_theme( $stylesheet );
-
 	if ( func_num_args() > 1 ) {
-		$template = $stylesheet;
 		$stylesheet = func_get_arg( 1 );
-	} else {
-		$template = $new_theme->get_template();
 	}
 
+	$old_theme = wp_get_theme();
+	$new_theme = wp_get_theme( $stylesheet );
+	$template  = $new_theme->get_template();
+
 	update_option( 'template', $template );
 	update_option( 'stylesheet', $stylesheet );
 
diff --git a/tests/phpunit/tests/theme.php b/tests/phpunit/tests/theme.php
index 972c964fa6..3c9b649ef8 100644
--- a/tests/phpunit/tests/theme.php
+++ b/tests/phpunit/tests/theme.php
@@ -85,6 +85,11 @@ class Tests_Theme extends WP_UnitTestCase {
 		$themes = get_themes();
 		// Generic tests that should hold true for any theme
 		foreach ( $themes as $k => $theme ) {
+			// Don't run these checks for custom themes.
+			if ( empty( $theme['Author'] ) || false === strpos( $theme['Author'], 'WordPress' ) ) {
+				continue;
+			}
+
 			$this->assertEquals( $theme['Name'], $k );
 			$this->assertNotEmpty( $theme['Title'] );