Index: src/wp-includes/template.php
===================================================================
--- src/wp-includes/template.php	(revision 41234)
+++ src/wp-includes/template.php	(working copy)
@@ -114,6 +114,11 @@
 	if ( count( $post_types ) == 1 ) {
 		$post_type = reset( $post_types );
 		$templates[] = "archive-{$post_type}.php";
+
+		// Prepend the hyphenated post type name as a higher priority template.
+		if ( strpos( $post_type, '_' ) ) {
+			array_unshift( $templates, 'archive-' . str_replace( '_', '-', $post_type ) . '.php' );
+		}
 	}
 	$templates[] = 'archive.php';