diff --git a/wp-includes/class-wp-theme.php b/wp-includes/class-wp-theme.php
index ad70a4bf9e..03368d31b5 100644
--- a/wp-includes/class-wp-theme.php
+++ b/wp-includes/class-wp-theme.php
@@ -228,7 +228,7 @@ final class WP_Theme implements ArrayAccess {
 		} elseif ( ! file_exists( $this->theme_root . '/' . $theme_file ) ) {
 			$this->headers['Name'] = $this->stylesheet;
 			if ( ! file_exists( $this->theme_root . '/' . $this->stylesheet ) )
-				$this->errors = new WP_Error( 'theme_not_found', sprintf( __( 'The theme directory "%s" does not exist.' ), $this->stylesheet ) );
+				$this->errors = new WP_Error( 'theme_not_found', sprintf( __( 'The theme directory "%s" does not exist.' ), esc_html( $this->stylesheet ) ) );
 			else
 				$this->errors = new WP_Error( 'theme_no_stylesheet', __( 'Stylesheet is missing.' ) );
 			$this->template = $this->stylesheet;
@@ -275,7 +275,7 @@ final class WP_Theme implements ArrayAccess {
 				$theme_root_template = $directories[ $this->template ]['theme_root'];
 			} else {
 				// Parent theme is missing.
-				$this->errors = new WP_Error( 'theme_no_parent', sprintf( __( 'The parent theme is missing. Please install the "%s" parent theme.' ), $this->template ) );
+				$this->errors = new WP_Error( 'theme_no_parent', sprintf( __( 'The parent theme is missing. Please install the "%s" parent theme.' ), esc_html( $this->template ) ) );
 				$this->cache_add( 'theme', array( 'headers' => $this->headers, 'errors' => $this->errors, 'stylesheet' => $this->stylesheet, 'template' => $this->template ) );
 				$this->parent = new WP_Theme( $this->template, $this->theme_root, $this );
 				return;
@@ -287,11 +287,11 @@ final class WP_Theme implements ArrayAccess {
 			// If we are a parent, then there is a problem. Only two generations allowed! Cancel things out.
 			if ( $_child instanceof WP_Theme && $_child->template == $this->stylesheet ) {
 				$_child->parent = null;
-				$_child->errors = new WP_Error( 'theme_parent_invalid', sprintf( __( 'The "%s" theme is not a valid parent theme.' ), $_child->template ) );
+				$_child->errors = new WP_Error( 'theme_parent_invalid', sprintf( __( 'The "%s" theme is not a valid parent theme.' ), esc_html( $_child->template ) ) );
 				$_child->cache_add( 'theme', array( 'headers' => $_child->headers, 'errors' => $_child->errors, 'stylesheet' => $_child->stylesheet, 'template' => $_child->template ) );
 				// The two themes actually reference each other with the Template header.
 				if ( $_child->stylesheet == $this->template ) {
-					$this->errors = new WP_Error( 'theme_parent_invalid', sprintf( __( 'The "%s" theme is not a valid parent theme.' ), $this->template ) );
+					$this->errors = new WP_Error( 'theme_parent_invalid', sprintf( __( 'The "%s" theme is not a valid parent theme.' ), esc_html( $this->template ) ) );
 					$this->cache_add( 'theme', array( 'headers' => $this->headers, 'errors' => $this->errors, 'stylesheet' => $this->stylesheet, 'template' => $this->template ) );
 				}
 				return;