diff --git a/lib/compat/wordpress-5.9/class-gutenberg-rest-templates-controller.php b/lib/compat/wordpress-5.9/class-gutenberg-rest-templates-controller.php
index 21b2a4d3a0ded6..085acca1d036d6 100644
--- a/lib/compat/wordpress-5.9/class-gutenberg-rest-templates-controller.php
+++ b/lib/compat/wordpress-5.9/class-gutenberg-rest-templates-controller.php
@@ -600,7 +600,7 @@ public function get_item_schema() {
 					'context'     => array( 'embed', 'view', 'edit' ),
 					'required'    => true,
 					'minLength'   => 1,
-					'pattern'     => '[a-zA-Z_\-]+',
+					'pattern'     => '[a-zA-Z0-9_\-]+',
 				),
 				'theme'          => array(
 					'description' => __( 'Theme identifier for the template.', 'gutenberg' ),